Measuring DIY two-part concentration?

[mcarroll]

Hoping to get some insight here.

I've been using DIY calcium and alkalinity components for a while now, and results are good but a little less consistent in the numbers than what I've been used to. I know there is variability in the anhydrous-ness of the Ca, so on the hunch that I may not be dosing the concentration that the math (and recipe) says I should be, I wanted to do some testing. Not sure if I'm going about this in a valid manner though.

What I've done is mix up a batch of Recipe 2. By the instructions this (about 200 grams) should give me a total of 18,500 ppm.

Would it be correct/accurate for me to dilute this down to the range of my Salifert Calcium test kit and take a reading with it? (I.e. will the lack of saltwater throw off the result to may it incomparable to my normal Ca tests?

Here's how I did it:
I started with 1 mL of 18,500 ppm solution
+1 mL RODI (=2 mL total) gets the solution down to 9,250 ppm.
+2 mL (=4 mL) gets to 4,750 ppm.
+4 mL (=8 mL) gets to 2,375 ppm.
+8 mL (=16 mL) get to 1187 ppm.
+16 mL (=32 mL) gets to 594 ppm.
+32 mL (=64 mL) gets to 296 ppm.

After testing the diluted sample I ended up with a reading about 10% lower than what I expected. This is packaged and sold as road salt so isn't hermetically sealed - like a Reef Crystals bucket would be, for example.

I weigh my reagents, so I'm guessing this 10% is mostly attributable to moisture, which would throw off the weight by at least some degree. Looking at the Reef Chemisty Calculator and comparing the mix rates for Dow Flake and Peladow (which have more and less moisture, respectively) kinda confirms this for me to at least some degree.

I'll be mixing at least 10% stronger than the anhydrous mix for Recipe 2 in the future.

Thanks in advance for any thoughts/corrections!

-Matt

 

[mcarroll]

Bump!

 

[mcarroll]

Prime-time bump instead of 3am?

 

[revsgirl]

:bump2:

 

[mcarroll]

One more 3am bump.


I'll add that I noticed in the Salifert Calcium kit's instructions it is claimed to be able to test in fresh/salt/whatever, so my question is definitely less about the kit.

Mostly I'd love a sanity check - is my method correct?

 

[mcarroll]

I need to re-run my test procedure on the next batch I make to see what concentration I'm actually making again.

I'm still living off the same 5 gallon bucket of CaCl (1.5+ years later), but I just confirmed in dailyweekly testing that my calcium part appears to be significantly less than full strength.

I actually noticed this a while ago and figured I goofed on the measurement or was misremembering the formula, so before mixing the gallon I'm just finishing with I re-read the Recipe #2 instructions and made sure what I was doing matched. Yet I'm still significantly behind on Ca levels again at the end of the jug.

Calcium chloride is extremely hygroscopic, so I suspect my weight per density of CaCl has gone up, skewing my measurements - I weigh my reagents. Spoilage!! This just means that in the future I will have to mix it according to the Dow Flake recipe (hopefully) or maybe test every batch as in the first post.

Will get my levels squared up again and probably will have to make a new batch of Recipe #2 calcium after that. When I do, I'll be back with some reportage.

More to come!

-Matt

 

[redfishbluefish]

Matt, let me throw in my two cents…..


I really don’t care about the actual equivalence of calcium in my DIY Calc solution. I do want consistency, but the actual concentration….10%, 15% percent either way doesn’t concern me. The reason is that I test my tanks Alk and Calc level weekly and adjust my dosing pumps to provide the desired concentrations in my tank. If by chance the calc solution I made was a little “weak,” then I’d end up putting in slightly more calc solution into the tank. So again, the actual concentration of my stock calc solution is rather moot.


As far as the cause of a slight change in expected concentration of a calcium chloride solution, it could be from the variation in hydration of this chemical. It is supplied in anhydrous form, monohydrate, dihyrate, tetrahydrate, hexahydrate, and possibly more. With most suppliers, you don’t know what you're getting and in what combination you have with the various “hydrated” forms. Especially with the anhydrous form, it is hydroscopic and will be constantly picking up water from the air. If you’re measuring weight, this could be throwing you off.

I’ve been using Prestone Driveway Heat and have had good luck with recipe 1, adding two cups to one gallon of RO/DI. I am currently using equal amounts of alk and calc on my tank, plus or minus a minute difference in the dosing pumps.

So again, it’s my tank’s calc level that I’m interested in and not the actual concentration of the stock calc solution.

 

[mcarroll]

I can see how you could make that work! The mixing error "rolls down hill" til it's caught in testing and the pumps are adjusted (approximately) accordingly. I guess that's sorta how I noticed this problem in the first place.

When you are dosing manually (which I am, now) it's awfully handy to be able to measure the correct amount to dose. I would think so in other times as well. I think in any event you won't have as stable a system if you aren't dosing known concentrations of chemicals. I guess it just feels right to nip the problem in the bud.

This is the whole basis and reason for being of the Reef Chemistry Calculator, after all - to be able to correctly mix and use these chemicals.

I use that to create my stock solutions and to calculate corrective doses. And really, it's not hard to run the test as described, and it's not something you'd have to do often - maybe only once, if my stock was sealed up better - it's in a road-salt bucket. (Tell me there isn't a cost to being cheap!! LOL) But why not test, then you have verified that your stock solution mix is correct (or not)? When they are correct, you can dose ca and alk 1:1 - one of the main ideas in the formulation of two-part - and not worry.

And you may have missed, I didn't notice a small discrepancy, I noticed a pretty big one. Exactly how big is the question to be answered* :nerd:, so I can once again correctly mix my stock solution...will be finding out tonight, with any luck.

-Matt

* If I were as diligent in testing and logging as I've been in the past, I'd already know my answer. Sadly, I'm not 100% sure of the quantity of doses or number of days since the last tests I did. I should still know after mixing another sample of stock solution and testing it tonight...

 

[mcarroll]

When I mixed for anhydrous (194g of reagent) I got a Ca test reading of 225 ppm. When I mixed it for dihydrate (256g of reagent) I got a test reading of 350ppm.

I think mathematically it should have been about 289ppm.

My Ca salt is about halfway converted to dihydrate. LOL.

So what I know now due to testing this is that I have a gallon of stock solution about 20% stronger than Recipe 2 is supposed to be.

Until I run out of this jug, I just remember to dose 20% less of my Ca solution. After that, I'll mix up (194g + 20% =) 232g of reagent per gallon of water.

-Matt