Dosing Nitrate and Phoshate.. Could use some help.

[Mykesocalreef]

I purchased some Loudwolf Sodium Nitrate and Trisodium Phosphate. I want to make solutions to dose. I have a standard food scale that will measure in grams but only to the whole gram. Do I need to get a more precise scale? Also looking for a good formula for each. My phosphates are currently .02 per red sea phosphate kit and the nitrate is not registering. I feed a lot. Currently no skimmer running. I just plumbed two tanks together and that might have bottomed out my nitrates. They usually sit about the 4ppm range. Any help would be appreciated. Thank you!

 

[Mjrenz]

Bump

 

[Dan_P]

I purchased some Loudwolf Sodium Nitrate and Trisodium Phosphate. I want to make solutions to dose. I have a standard food scale that will measure in grams but only to the whole gram. Do I need to get a more precise scale? Also looking for a good formula for each. My phosphates are currently .02 per red sea phosphate kit and the nitrate is not registering. I feed a lot. Currently no skimmer running. I just plumbed two tanks together and that might have bottomed out my nitrates. They usually sit about the 4ppm range. Any help would be appreciated. Thank you!

Are you asking for the molecular weight of each salt or the weight of each salt to make a certain concentration to dose?

 

[Dkeller_nc]

Sodium Nitrate: 85 grams/mol, of which the nitrate portion is 62 grams/mol. So if you make a 1 liter solution of 85 grams of sodium nitrate, each 10 mL of this solution will have 0.62 grams of nitrate. If you dose that 10 mL into 100 gallons of seawater, it will raise that seawater's nitrate concentration by 620 milligrams/378.5 liters x (1ppm/1 mg/L) = 1.64 ppm.

Trisodium Phosphate: 164 grams/mol, of which the phosphate portion is (164 grams - 3x(23 grams/mol Na) = 95 grams/mol. So if you make a 1 Liter solution of 164 grams of trisodium phosphate, each 10 mL of this solution will have 95 grams/100 = 0.95 grams of phosphate. If you dose that 10 mL into 100 gallons of seawater, it will raise that seawater's phosphate concentration by 950 milligrams/378.5 liters x (1ppm/1 mg/L) = 2.51 ppm.

There's a problem with trisodium phosphate, however. It's hygroscopic, and while what you bought me be anhydrous, it could also have as much as 12 mol of water in the compound per mol of trisodium phosphate. That will change the calculation significantly; trisodium phosphate dodecahydrate has a molecular weight of 380 grams/mol, of which the phosphate portion is again 95 grams/mol.

So if you assume the compound is anhydrous, and make up a solution that's 164 grams in 1 liter, you'll actually have a solution that's considerably less concentrated than the former example. In this case, the solution will have 41 grams of phosphate in that 1 liter, and dosing 10 mL of it into 100 gallons will result in an increase of 1.08 ppm.

Note - I gave the above figures for simplicity's sake so that you can see how I derived the answer. In the case of the sodium nitrate, it's extremely soluble in water, so you'd have no problem dissolving 85 grams in 1 liter of water. In the case of trisodium phosphate, it's not nearly as soluble as my example would suggest. Specifically, anhydrous trisodium phosphate has a solubility of about 120 grams per liter at 20 deg C. The dodecahydrate form has a solubility of about 283 grams in 1 liter at 20 deg C.

So, you'll want to try a solution at about 1/2 the strength that I noted - about 82 grams per liter. If it's anhydrous, that 10 mL dose will raise the 100 gallons of seawater (you guessed it) by about 1.25 ppm. If it's the dodecahydrate, about 0.54 ppm.

You may have to adjust these concentrations according to your needs. If you do indeed have about 100 gallons of total volume, and you only want to raise the phosphate concentration by about 100 ppb, you'll want to dissolve about 8 grams of the trisodium phosphate in 1 liter of water (and you can still dose 10 mL). If, for example, you only have 25 gallons, you might want to cut the concentration by 4 so that you can still dose 10 mL (easy to measure) versus 2.5 mL (harder to measure).

 

[Mykesocalreef]

Are you asking for the molecular weight of each salt or the weight of each salt to make a certain concentration to dose?

looking for the weight/amounts to make up a standard mixture. How many grams per liter for a stock concentration.

 

[Gareth elliott]

I use this calculator https://rotalabutterfly.com
Select kh2po4 and kno3 for the chemicals used they will be very close to the chemicals you are using and off by only a percentage or 2 which is irrelevant in the end.

 

[Mykesocalreef]

Sodium Nitrate: 85 grams/mol, of which the nitrate portion is 62 grams/mol. So if you make a 1 liter solution of 85 grams of sodium nitrate, each 10 mL of this solution will have 0.62 grams of nitrate. If you dose that 10 mL into 100 gallons of seawater, it will raise that seawater's nitrate concentration by 620 milligrams/378.5 liters x (1ppm/1 mg/L) = 1.64 ppm.

Trisodium Phosphate: 164 grams/mol, of which the phosphate portion is (164 grams - 3x(23 grams/mol Na) = 95 grams/mol. So if you make a 1 Liter solution of 164 grams of trisodium phosphate, each 10 mL of this solution will have 95 grams/100 = 0.95 grams of phosphate. If you dose that 10 mL into 100 gallons of seawater, it will raise that seawater's phosphate concentration by 950 milligrams/378.5 liters x (1ppm/1 mg/L) = 2.51 ppm.

There's a problem with trisodium phosphate, however. It's hygroscopic, and while what you bought me be anhydrous, it could also have as much as 12 mol of water in the compound per mol of trisodium phosphate. That will change the calculation significantly; trisodium phosphate dodecahydrate has a molecular weight of 380 grams/mol, of which the phosphate portion is again 95 grams/mol.

So if you assume the compound is anhydrous, and make up a solution that's 164 grams in 1 liter, you'll actually have a solution that's considerably less concentrated than the former example. In this case, the solution will have 41 grams of phosphate in that 1 liter, and dosing 10 mL of it into 100 gallons will result in an increase of 1.08 ppm.

Note - I gave the above figures for simplicity's sake so that you can see how I derived the answer. In the case of the sodium nitrate, it's extremely soluble in water, so you'd have no problem dissolving 85 grams in 1 liter of water. In the case of trisodium phosphate, it's not nearly as soluble as my example would suggest. Specifically, anhydrous trisodium phosphate has a solubility of about 120 grams per liter at 20 deg C. The dodecahydrate form has a solubility of about 283 grams in 1 liter at 20 deg C.

So, you'll want to try a solution at about 1/2 the strength that I noted - about 82 grams per liter. If it's anhydrous, that 10 mL dose will raise the 100 gallons of seawater (you guessed it) by about 1.25 ppm. If it's the dodecahydrate, about 0.54 ppm.

You may have to adjust these concentrations according to your needs. If you do indeed have about 100 gallons of total volume, and you only want to raise the phosphate concentration by about 100 ppb, you'll want to dissolve about 8 grams of the trisodium phosphate in 1 liter of water (and you can still dose 10 mL). If, for example, you only have 25 gallons, you might want to cut the concentration by 4 so that you can still dose 10 mL (easy to measure) versus 2.5 mL (harder to measure).

Thank you so much for the reply. Yeah chemistry in high school was not my strong point. Thank you for the help. Is there a way to tell which trisodium phosphate I have?

 

[Dkeller_nc]

Thank you so much for the reply. Yeah chemistry in high school was not my strong point. Thank you for the help. Is there a way to tell which trisodium phosphate I have?

That I'm aware of, not easily. Baking a chemical like that and monitoring the drop in weight is something I've the equipment to do in a lab at work, and it can be done by chemical means with something like thionyl chloride, but this is not something you should try at home. The difficulty with drying it in an oven is that water of hydration have very different reaction equilibria depending on the actual compound. So the actual temperature required for driving off water of hydration would be quite different depending on the actual compound, and I don't have any equilibrium data on trisodium phosphate to tell you what that temperature would be, and whether polyphosphates would be formed at higher temperatures.

My advice would simply be to assume that the compound is the anhydrous form, make the solution at the strength that you think that you need, and monitor the results in your aquarium with an appropriate phosphate test. Since I'd presume that underdosing would be inconvenient but not of any real consequence for your aquarium, while overdosing would be potentially bad, you should choose the most conservative option, which is to assume the material is anhydrous trisodium phosphate. If your phosphate test indicates that you're underdosing, no big deal, just add more.

 

[Mykesocalreef]

@Dkeller_nc I think I have the grasp of the Sodium Nitrate, if I did the math right. With your ratio and my tank being 190 gallons ever 10ml will be .86ppm of nitrate? The phosphate one has me all sorts of confused. Yes I want to be conservative to under dose instead of over. Could you please help with the phosphate math. Also understanding I should cut the dose in half so it dissolves easier? Thanks again for your help its much appreciated.

 

[Dkeller_nc]

So since your system volume is 190 gallons, that's 719 liters. If you dose 10 mL of the sodium nitrate solution mentioned above, you will raise the nitrate concentration of the water by 620 mg/719L = 0.86 ppm (so yes, you're correct).

For phosphate, let's assume you're going to make a solution of 82 grams of the trisodium phosphate that you have in 1 liter of water. That's well under the solubility limit, so that should dissolve, though it may take a good bit of stirring. If you dose 10 mL of that solution into your system, the maximum increase in phosphate in the tank water will be 475 mg/719L = 0.66 ppm. That's if the trisodium phosphate that you have is anhydrous. If it's the dodecahydrate form, you will get a rise in the phosphate concentration of 205 mg/719L = 0.29 ppm.

I suppose I should've asked at the first part of this discussion - how much do you want to raise the nitrate and phosphate concentration in your tank(s) in ppm, and what amount of liquid do you think is reasonable and easy for you to measure and dose?

 

[Mykesocalreef]

According to my tests via Red Sea, Nitrate is 0 I would like it to be in the 5-10ppm. Phosphate is .02, would like it .02-.04ppm range. I don't really have any lab grade dosing containers. I do have the BRS containers that come with their 2 part. I believe they are in 5ml increments. I really appreciate the help!

 

[Dkeller_nc]

OK, first thought is that getting decently accurate measuring containers is pretty cheap. Since I'm a scientist, I gravitate towards laboratory glassware - 1 and 2 liter volumetric flasks and 10 mL and 100 mL graduated cylinders are what I use most often. They used to be really expensive back in the day, but no longer - you can get a 1 liter class-A volumetric flask off of Amazon for about $20 if you choose to go that route. If you do go this route, realize that volumetric flasks are impossible to mix without a magnetic stir bar and a magnetic stir plate. Fortunately, these are also a heck of a lot cheaper than they used to me.

Alternatively, you can certainly use a large glass kitchen liquid measuring cup, ideally of at least 1 quart capacity. For this purpose, I don't think I'd recommend your average "gallon" plastic jug unless you're willing to calibrate it by pouring a measured amount of liquid in it and permanently marking it.

For dosing, the little graduated tri-pour graduated plastic beakers are exactly what I use - they're reasonably accurate (I checked) and they're unbreakable.

OK, since you have those containers, we'll shoot for a 50 mL dose at a time, since that's easy to measure. Next question - how much do you want to bring your levels up at a time? All in one dose? If so, we'll calculate how much to dissolve to do that with your system volume all in one 50 mL dose. If you want to do this more incrementally, we can lower the concentration of the stock solution, and you can do it in 2, 3, 4, 5 or however many doses spread out over X days that you wish.

 

[Mykesocalreef]

I'm going to hunt down some of those products you mentioned on Amazon. I like to gradually raise so there are no large swings, over three days is usually my time frame.

 

[Dkeller_nc]

OK, so let's do the equations backward to come up with your preferred dosing.

In the case of phosphate, you want to raise the phosphate of the 719 L system volume by 10 ppb per 50 mL dose, 2 doses to get an increase of 20 ppb (0.02 ppm).

Therefore, for each dose of 50 mL of solution, we need it to contain 719Lx0.01ppmx (1mg/mL/1 ppm) = 7.19 mg of phosphate ion. Then to calculate the amount of trisodium phosphate (anhydrous) we need to dissolve in 1 Liter to make this solution, 7.19mg/50mL*(164mgNa3PO4/95mgPO4)=0.248 mg Na3PO4/mL. That's per milliliter. Since we want to make 1 liter, multiply by 1000 to get to 248 mg of Na3PO4 (trisodium phosphate) required per liter of solution.

You're either going to have to use an analytical balance to measure the ~250 mg you'll need to make this solution, or you're going to have to make it 10 times more concentrated (2.5 g/L) and make a 1:10 dilution of it in a second 1 L volumetric flask.

Needless to say, this is sort of inconvenient, but the reason for this is that you're probably trying to do something that isn't really practical, which is increase the phosphate concentration of your tanks by 20 parts per billion from 20 parts per billion to 40 parts per billion. Not only are those levels quite low (though there are some reefers that still target <50 ppb), you really don't have the ability accurately measure the change; I think Hanna's ULR Phosphorus Checker, at best, is +/- 5 ppb, and I personally find that level of precision and accuracy to be highly suspect.

At any rate, here's the breakdown for the Nitrate part that you want to do. Because you're adding a great deal more nitrate than phosphate, it's practical to break this up into three 50mL doses. I'm going with a 5ppm NO3 increase - you can double the number of doses if you want to get to 10ppm.

So, for 719L to 5 ppm, we need 3,595 mg of NO3 ion. That equates to 3,595mg*85mg NaNO3/62 mg NO3 = 4,929 mg. We want to break that up into 3 50mL additions, so each 50mL addition needs 4,929mg/3 = 1,642.9 mg NaNO3. That means that you need to make up 1 Liter of 1,642.9mg NaNO3/50mL*1000mL/1L = 32,857 mg of NaNO3, or 32.9 grams of sodium nitrate per liter.

 

[Mykesocalreef]

Here is a screenshot let me know your opinion on these. What is your opinion on a healthy level of Phosphate? I have read that up to .1 ppm shouldn't cause any harm. With the numbers you provided it does seem inconvenient to raise by .02. I just want to make sure I can get a detectable reading without overdosing. Again I really appreciate your time and help with this. Thank you!

 

[PatW]

I dose nitrate and phosphate.

I use reagent grade sodium nitrate.... amazon’s version of it. I could get an accurate scale but I decided to go by guess and by gosh first. This ain’t rocket science.

Nitrate stock solution: half a cup of sodium nitrate in one gallon of RODI. I dose 2 tablespoons per day into a 300 gallon with chaeto and a skimmer to maintain 1 ppm nitrate. I have not tried to see what I need to add to take 0 to 1 ppm for some time. It Probably takes 4 tbs to do it.

I use reagent grade trisodium phosphate. I only open the bottle to dose and that in air conditioning and only very briefly. So far, it has stayed dry. For my phosphate stock solution, I add 2 tbs of trisodium phosphate to 1 gallon of RODI. I dose 2.5 tablespoon of the stock to maintain about .02 ppm phosphate. By .02, I mean 24 hours after dosing. I think right after dosing, my system hits something like .04. The system really sucks up phosphate.

My quick and dirty approach works for me. In my laboratory days, I would have weighed the chemicals on a super accurate scale and used volumetric flasks and dosed precise amounts.

But my system does not care. As long as the nitrates are between .75 and 2 ppm, it is happy. I bet it would be happy with between .5 and 5 ppm. For phosphates, it seems to want measurable phosphates to something not too high so something like between .003 and .05 ppm would probably work.

 

[Sod Buster]

I want to know if this is anhydrous version also. And a cheap accurate amazon scale.

 

[Dkeller_nc]

Here is a screenshot let me know your opinion on these. What is your opinion on a healthy level of Phosphate? I have read that up to .1 ppm shouldn't cause any harm. With the numbers you provided it does seem inconvenient to raise by .02. I just want to make sure I can get a detectable reading without overdosing. Again I really appreciate your time and help with this. Thank you!

All of these items will be perfectly suitable for a small home lab if that's your thing, although I'd say you might not have all that much use for the beakers and the smaller graduated cylinders. One thing to know - volumetric flasks and graduated cylinders are made for measuring liquids in the laboratory, and they're accurate, with the volumetric flask good to about +/- 2%, and the graduated cylinders to about +/- 5%. While the beakers are graduated, they are typically not calibrated, and it will say right on the beaker "volumes are approximate", so us lab geeks use then as convenient containers. But as I'm sure you've discovered, labware is far, far cheaper than it was in the 1980's when I had to pay up if I broke something in Organic Chemistry Lab, so there's certainly no harm in having it around, except for the neighbors wondering if you're up to no good.

The magnetic stir plate, in my opinion, is a must-have for one and only one reason, though other uses are "nice to have", and that's dissolving up sodium bicarbonate for the alkalinity part of 2-part dosing solutions. I make mine at 78 grams/Liter, which is close to the solubility limit. Without the stir plate, a volumetric flask and a stir bar, I'd either have to heat the RODI water significantly, or stand there and stir the solution for 10 to 15 minutes (or shake it in a jug) to get everything dissolved. With the stir plate, it's pour the volumetric 2/3rds full of RODI, add the sodium bicarbonate through a funnel, start it stirring, add the rest of the water to the line, and just let it do its thing for 30 minutes. When I walk back into the room, the solution's crystal clear with virtually no effort on my part.

By the way - If you do decide on the lab glassware route, you will need a plastic funnel to get powders into the volumetric, and you want something called a "powder funnel"; doing that with a spoon's a real drag. Ironically, most of the plastic funnels you find for sale at the grocery store are powder funnels, so you need not buy those from a sceintific supply house. You can make a single-use funnel out of wax paper rolled into a cone shape in a pinch, as well.

Finally, about the phosphate level - you will get a raging argument back and forth on what's "optimal" for an SPS reef. In Richard Ross' case, it's about 1-3 ppm. In my case, anything below 0.3 ppm and above 0.1 ppm is good. I keep my nitrates at about 10ppm. But I keep a lot of wild corals, as I'm just not into the "named coral frag" thing. And I can tell you from first-hand unhappy experience that wild corals do not appreciate really low nutrients.

I answered your original question directly because that's what you asked for, and also to show you how to do your own calculations if you wish. There's a fair amount of:

Original Poster: How do I do X?
Forum Respondent #1: Why on earth would you want to do X? You should do Y!
Original Poster: But I really want to do X....
Forum Respondent #2: Forget what FR#1 said, you really, really should do Z!

And so on 'net forums.

I'd be one of those forum respondents if someone asked how to do something dangerous to either themselves or their animals, but supplementing dissolved nutrients isn't one of those cases. And Pat's absolutely correct - I do relatively high precision solutions because I've been doing it that way since I was 13, and it's second nature. But I'll be the first to tell you that for this purpose, it's definitely not necessary. You absolutely can do it with ordinary kitchen equipment, and simply test to see where you're at once you've dosed a little. The only thing you need to do is get in the ballpark to make sure you're not jacking your nitrate levels from 0 to 100 ppm in one dose.

 

[Mykesocalreef]

@Dkeller_nc
Once I make the solutions are they safe to store in a plastic container?

 

[Dkeller_nc]

Yes, though I'd choose a polyethylene container such as the kind that vinegar comes in just to ensure that nothing leaches from the container into the solutions you're dosing.