pH, alkalinity, and calcium question

[kdx7214]

So I just bought a Hanna checker for both calcium and alkalinity. Right now my tank is sitting at 7.82 ph, 13.7 dkh, and 443 ppm calcium. I am thinking my pH is too low. I have two sps and have read that ph should be in the 8.3 to 8.5 range. I've been reading the article below. It's a DIY mix. Is this still valid and workable or should I do something else?

http://reefkeeping.com/issues/2006-02/rhf/index.php#3

On another note, how do I adjust the ph without mucking up the other readings? I've tried baking soda, but it tops out at 7.89.

Thanks!

 

[Privateye]

If your alkalinity is high and your pH is low, try adding additional aeration. CO2 will form carbonic acid and lower your pH, but not your alkalinity

 

[A_Blind_Reefer]

Ugh,, I wish they would stop coming out with these ph numbers. I’ve seen as high as 8.9 being touted as a target ph. My opinion is worth nothing so factor that, but your ph is on the lower end of perfectly fine. I’d be a bit more concerned with your Alk. It is higher than most would say is acceptable. That’s just me though.

edit. That baking soda you added probably raised your alk

 

[Privateye]

8.3 is what baking soda will buffer to. Realistically you'll always have some CO2 in there. Personally I'm comfortable at 7.9 but ideally I like 8.0-8.2. It's worked for me at least.

 

[kdx7214]

I guess I will go throw some baking soda in the oven for a while then try to get the ph up some more. I'm going to try to get more aeration in the tank, but how to do it without leaving salt splatters everywhere is another problem entirely. Anyone have any ideas on that?

Edit: I just realized why people have trouble balancing these things. If you increase aeration, you produce carbonic acid from the CO2 in the air, which lowers ph. The lower ph lowers the alkalinity by reacting with the acid. Not quite sure how to balance all this without screwing something else up. Hmmm.

 

[A_Blind_Reefer]

I guess I will go throw some baking soda in the oven for a while then try to get the ph up some more. I'm going to try to get more aeration in the tank, but how to do it without leaving salt splatters everywhere is another problem entirely. Anyone have any ideas on that?

Edit: I just realized why people have trouble balancing these things. If you increase aeration, you produce carbonic acid from the CO2 in the air, which lowers ph. The lower ph lowers the alkalinity by reacting with the acid. Not quite sure how to balance all this without screwing something else up. Hmmm.

At 13.7dkh I’m not sure I would add any soda ash!

 

[Privateye]

I guess I will go throw some baking soda in the oven for a while then try to get the ph up some more. I'm going to try to get more aeration in the tank, but how to do it without leaving salt splatters everywhere is another problem entirely. Anyone have any ideas on that?

Edit: I just realized why people have trouble balancing these things. If you increase aeration, you produce carbonic acid from the CO2 in the air, which lowers ph. The lower ph lowers the alkalinity by reacting with the acid. Not quite sure how to balance all this without screwing something else up. Hmmm.

Sort of, but that's a little backwards if you have elevated CO2. Aeration off-gases CO2 when it's elevated. The same process that gets oxygen into the water gets CO2 out in most aquatic systems. If the water had no CO2 in it then aeration would add it, but CO2 never gets close to saturation in aquatic environments. It always sits far below saturation, unlike O2 which can easily reach saturation (or close to it) with sufficient aeration.

I'm basically saying you might have too much CO2 in your water, and if so aeration can fix that. Weak acids like carbonic acid will lower your pH but not your alkalinity. Strong acids will reduce both. Your alkalinity is quite high compared to your pH so CO2 would be the first thing I'd look into.

Edit: I've seen pH jump as high as 0.3 just from moving the air intake of a protein skimmer from inside the house to outside. Within hours.

 

[kdx7214]

Sort of, but that's a little backwards if you have elevated CO2. Aeration off-gases CO2 when it's elevated. The same process that gets oxygen into the water gets CO2 out in most aquatic systems. If the water had no CO2 in it then aeration would add it, but CO2 never gets close to saturation in aquatic environments. It always sits far below saturation, unlike O2 which can easily reach saturation (or close to it) with sufficient aeration.

I'm basically saying you might have too much CO2 in your water, and if so aeration can fix that. Weak acids like carbonic acid will lower your pH but not your alkalinity. Strong acids will reduce both. Your alkalinity is quite high compared to your pH so CO2 would be the first thing I'd look into.

Thanks for the added detail. I'll see what I can do about reducing the CO2 levels. Not quite sure how yet, but I'll figure something out. Thanks!

 

[arking_mark]

Assuming your tank aeration is adequate, your in home air quality is in the normal range, and your Alk measurement is in the ballpark, your pH measurement accuracy is off.

To get 7.82 NBS pH with 13ish dKH, your indoor CO2 air quality would be around 2000...which would cause human health issues with extended exposure.

Below is the mathematical model that shows the calculations:

You can do a simple cup aeration test with outdoor air (400ppm CO2) to see how accurate your measurement are. Just take a cup of tank water and aerate it with an airstone for an hour outside. You should measure 8.46ish.

 

[Randy Holmes-Farley Verified Community Expert]

Ugh,, I wish they would stop coming out with these ph numbers. I’ve seen as high as 8.9 being touted as a target ph. My opinion is worth nothing so factor that, but your ph is on the lower end of perfectly fine. I’d be a bit more concerned with your Alk. It is higher than most would say is acceptable. That’s just me though.

edit. That baking soda you added probably raised your alk

IMO, that 8.9 is a serious mistake and I think someone noted that they guy promoting it later discovered the problem:excessive precipitation of calcium carbonate.

 

[Randy Holmes-Farley Verified Community Expert]

Sort of, but that's a little backwards if you have elevated CO2. Aeration off-gases CO2 when it's elevated. The same process that gets oxygen into the water gets CO2 out in most aquatic systems. If the water had no CO2 in it then aeration would add it, but CO2 never gets close to saturation in aquatic environments. It always sits far below saturation, unlike O2 which can easily reach saturation (or close to it) with sufficient aeration.

I'm basically saying you might have too much CO2 in your water, and if so aeration can fix that. Weak acids like carbonic acid will lower your pH but not your alkalinity. Strong acids will reduce both. Your alkalinity is quite high compared to your pH so CO2 would be the first thing I'd look into.

Edit: I've seen pH jump as high as 0.3 just from moving the air intake of a protein skimmer from inside the house to outside. Within hours.

Just a clarification to that discussion.

Increased aeration can add or remove CO2 and thus lower or raise pH depending on whether the tank has more or less CO2 in it in relation to the air being used for aeration.

Both of those things can happen in the same tank at different times if the day (e.g., add CO2 during the day and release it at night).

 

[kdx7214]

Assuming your tank aeration is adequate, your in home air quality is in the normal range, and your Alk measurement is in the ballpark, your pH measurement accuracy is off.

To get 7.82 NBS pH with 13ish dKH, your indoor CO2 air quality would be around 2000...which would cause human health issues with extended exposure.

Below is the mathematical model that shows the calculations:

You can do a simple cup aeration test with outdoor air (400ppm CO2) to see how accurate your measurement are. Just take a cup of tank water and aerate it with an airstone for an hour outside. You should measure 8.46ish.

Hmm. I have a ph probe and a handheld tester that both show the same ph values (or within +/- 0.02). I'll take it outside and see what I get though. Thanks!

 

[Dburr1014]

I guess I will go throw some baking soda in the oven for a while then try to get the ph up some more. I'm going to try to get more aeration in the tank, but how to do it without leaving salt splatters everywhere is another problem entirely. Anyone have any ideas on that?

Edit: I just realized why people have trouble balancing these things. If you increase aeration, you produce carbonic acid from the CO2 in the air, which lowers ph. The lower ph lowers the alkalinity by reacting with the acid. Not quite sure how to balance all this without screwing something else up. Hmmm.

Airline to the skimmer from outside will do wonders!

 

[kdx7214]

Assuming your tank aeration is adequate, your in home air quality is in the normal range, and your Alk measurement is in the ballpark, your pH measurement accuracy is off.

To get 7.82 NBS pH with 13ish dKH, your indoor CO2 air quality would be around 2000...which would cause human health issues with extended exposure.

Below is the mathematical model that shows the calculations:

You can do a simple cup aeration test with outdoor air (400ppm CO2) to see how accurate your measurement are. Just take a cup of tank water and aerate it with an airstone for an hour outside. You should measure 8.46ish.

Not quite sure what equations that is using, but I just recalibrated everything and used a different Hanna checker and got the same results. pH is averaging 7.76 +- 0.02. As someone else suggested, I took an air pump and some tank water outside and let it aerate for about 20 minutes then did a pH test and came out with 8.0, which while better is still not in the 8.3 - 8.6 range I keep seeing recommended.

At this point I'm looking into ways to inject pure oxygen into the tank, rather than room air.

 

[Randy Holmes-Farley Verified Community Expert]

Not quite sure what equations that is using, but I just recalibrated everything and used a different Hanna checker and got the same results. pH is averaging 7.76 +- 0.02. As someone else suggested, I took an air pump and some tank water outside and let it aerate for about 20 minutes then did a pH test and came out with 8.0, which while better is still not in the 8.3 - 8.6 range I keep seeing recommended.

At this point I'm looking into ways to inject pure oxygen into the tank, rather than room air.

Hold up. Pure O2 will not raise pH, and O2 has almost nothing to do with pH in a reef tank. If you raise O2 to 4 or 5 times the normal level with pure O2, you may have serious issues.

Im not sure where you see folks recommending pH 8.3 to 8.6 as generally optimal. I recommend 7.8 to 8.5 with 8.1 to 8.3 being generally better.

 

[Sumo Reef]

IMO I would keep the pH and alk stable. Your readings are acceptable if they are stable, although IMO I would lower the alk from 13 to 11.

What are you seeing that makes you want to correct ph?

 

[kdx7214]

Hold up. Pure O2 will not raise pH, and O2 has almost nothing to do with pH in a reef tank. If you raise O2 to 4 or 5 times the normal level with pure O2, you may have serious issues.

Im not sure where you see folks recommending pH 8.3 to 8.6 as generally optimal. I recommend 7.8 to 8.5 with 8.1 to 8.3 being generally better.

So I'm just below the low end of what you recommend. How do I get the ph up a little bit so it's in a safer range?

 

[kdx7214]

IMO I would keep the pH and alk stable. Your readings are acceptable if they are stable, although IMO I would lower the alk from 13 to 11.

What are you seeing that makes you want to correct ph?

dang near everything I read online says 8.3-8.6 is the good range for sps. I'm topping out at 7.86 or so and hitting as low as 7.6 at night.

 

[Randy Holmes-Farley Verified Community Expert]

Fresher air to the room, low CO2 air to a skimmer inlet, more photosynthesis in the tank or a refugium, and the highest pH alk additives available all can help.

 

[Randy Holmes-Farley Verified Community Expert]

dang near everything I read online says 8.3-8.6 is the good range for sps. I'm topping out at 7.86 or so and hitting as low as 7.6 at night.

No, you must be reading articles who’s purpose is to maximize calcification/growth rate (assuming they have any idea what they are talking about).

That pH range is well above the ocean and no one ever claims corals cannot thrive at pH 8.1 to 8.2, which are typical ocean values.

I’d suggest looking for new sources of information, or for actual values from tanks you admire.