High pH. Help to reduce it? Using Kalk.

[wakerider017]

Hey guys.

Have had my 120G DT up and running for several months now.

I think I might be having some issues with the pH.


Several weeks ago before I was thinking about dosing kalk I added sodium carbonate (baked baking soda) to my system to increase Alk and also raise pH.
My pH was dancing from 8.00 to 8.20 daily which was probably pretty good, and my Alk was at an ultra low 5.5 dKH.)

The pH was raised to 8.20 - 8.40 and Alk was raised to 7.0 dKH. This pH was still probably pretty good, and my Alk was looking better, but still needed work.


In comes the kalk to take care of my Alk and Ca needs. I have my kalk being dosed from a kalk stirrer that is hooked up to my ATO. The ATO runs 24 times a day to keep the tank volume at a constant level. (My ATO delivers about 1.5 gallons per day)

The problem is I have to keep shutting off my ATO because of pH spikes. It is going over 8.5 and if I let it run I'm sure it would go even higher... 8.6,8.7, 8.8 maybe 8.9??


So I am asking advice from the chemistry experts... Should I try dosing vinegar to get the pH back down?

I'm really at a loss... :/

[bertoni]

You could dose some soda water to lower the pH if need be. Vinegar sometimes causes bacterial blooms, so we don't recommend it any more. I wouldn't bother at this point.

Aeration will lower the pH fairly rapidly in most systems. Does the tank have a skimmer? What kind of pump is delivering the Kalk? Is it a peristaltic pump? The safest way to dose Kalkwasser is a pump that delivers a series of drops, rather than adding a lot of Kalkwasser in one shot.

[wakerider017]

You could dose some soda water to lower the pH if need be. Vinegar sometimes causes bacterial blooms, so we don't recommend it any more. I wouldn't bother at this point.

Aeration will lower the pH fairly rapidly in most systems. Does the tank have a skimmer? What kind of pump is delivering the Kalk? Is it a peristaltic pump? The safest way to dose Kalkwasser is a pump that delivers a series of drops, rather than adding a lot of Kalkwasser in one shot.

Thanks for the quick reply!


- regular soda water purchased at the grocery store?

-Yes, tank has a skimmer. skimmer output has been designed to reduce and water disruption or bubbles, so maybe I will adjust that real quick.

-kalk pump is an aqualifter. (was trying to save money). I was looking at the BRS pumps.. I guess the 50ml per min pump would be ideal for this system. what do you recommend?

-what ph range should i try to target? 8.1-8.4 swing for the day??

[Randy Holmes-Farley]

yes, regular soda water, if you are confident that the pH is high.

This has more:

High pH: Causes and Cures
http://reefkeeping.com/issues/2005-03/rhf/index.htm

[wakerider017]

Looks like I'll be running to the grocery store tmrw. I'll report back.


But in the meantime, with kalk, what can I expect as a normal pH shift.

As stated I have a 120G DT with just a few corals and a bunch of live rock. 40 gallon sump below. Lights on 8 hours a day. Want to add approx 1.5 gallons of concentrated limewater everyday.

before kalk my swing was around .2pH. Thanks!

[bertoni]

I used a MasterFlex peristaltic pump when delivering Kalk. Any decent peristaltic pump should be okay, though. I don't know much about what's on the market. For that size tank, a 50 ml per shot pump might be fine.

The pH shift is hard to predict, since it's based on a number of factors, with the oxygenation rate being one of the more important.

[tmz]

If the stirrer is coming on 24 times a day ,it's likely cloudy water is being dosed which contains undissolved kalk( calcium hydroxide) that hasn't had a chance to settle out.

If so,this extra undissolved calcium hydroxide will dissolve when it hits a larger volume of water,ie the tank, leading to an overdose and a ph spike.

In this case more calcium hydroxide is being dosed than fully saturated lime water would hold and more is being dosed at any given time than planned. CO2 entering the tank water from the air will equilibriate but needs time .So it's important to insure the increments of kalk dosed are small and spread over a long period of time.

[Coasterfrk]

I'm having a very similar problem right now. My kalk topoff controlled by brs 50ml doser and Apex is programmed to stop the top off if ph gets to 8.4. The ph basically stays there all the time thus my top off does not add enough water to keep up with evaporation.


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[wakerider017]

If the stirrer is coming on 24 times a day ,it's likely cloudy water is being dosed which contains undissolved kalk( calcium hydroxide) that hasn't had a chance to settle out.

If so,this extra undissolved calcium hydroxide will dissolve when it hits a larger volume of water,ie the tank, leading to an overdose and a ph spike.

In this case more calcium hydroxide is being dosed than fully saturated lime water would hold and more is being dosed at any given time than planned. CO2 entering the tank water from the air will equilibriate but needs time .So it's important to insure the increments of kalk dosed are small and spread over a long period of time.

The water looks mostly clear, but maybe I'll put the stirrer on a separate timer that only runs a couple of times per day. (It will have to be a manual timer since I am out of spot on my Apex EB8).

Good suggestion! Thanks!

I'm having a very similar problem right now. My kalk topoff controlled by brs 50ml doser and Apex is programmed to stop the top off if ph gets to 8.4. The ph basically stays there all the time thus my top off does not add enough water to keep up with evaporation.


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Yup, we are in the same boat. No fun!!

[travis32]

Right now I'm going with a swing from 7.98, to 8.4 ph a day. I go based on how things look in my tank, if I see anything receding I look for the cause, if things appear happy, then, they've adapted to the ph swings.

Probably not very scientific. I'm running at around a year and a half with decent ph swings.

[Randy Holmes-Farley]

IMO those pH values (anything up to a bit over 8.5) is OK, IMO.

[JDuong916]

Randy Holmes,

Could you add soda water directly to limewater, lowering the PH of the solution before it reaches the display tank?

Another question, why does adding CO2 lower PH? I thought if you add H+ PH goes down. How does CO2 play into this? Sorry, I wish I studied a little harder in my chemistry classes 😉

[JDuong916]

Never mind the second question. You've already answered it in the link previously provided.

[Randy Holmes-Farley]

No, you cannot add CO2 to limewater. You'll produce insoluble calcium carbonate.

[Jimmy54]

Another question, why does adding CO2 lower PH? I thought if you add H+ PH goes down. How does CO2 play into this? Sorry, I wish I studied a little harder in my chemistry classes ��

Limewater is Ca(OH)2

CO2 + Ca(OH)2 => CaCO3 + H2O ;)

CO2 + H2O <=> H2CO3 <=> H+ HCO3 <=> H+ H+ CO3 :)

[JDuong916]

Thanks for the replies. I'm still having trouble keeping my pH down while using limewater. Might have to go back to dosing two part.

[Randy Holmes-Farley]

How high does it get?

[tmz]

Sprung and Delbeek in The Reef Aquarium Vol3 recommend a maximum kalk dose of 1/4 tsp(1.25 grams) of kalk per 50gallons(189 liters) of aquarium water volume per hour as a general guideline to avoid pH spikes. At this rate there is typically enough time for CO2 from the air entering the water to make up the CO2 used by the kalkwasser/limewater as it forms carbonate.

Dosing 473 of milliters ( 16 ounces ) of clear limewater mixed at 2 tsps per gallon or less per hour per 50 gallons of aquarium water volume stays within that limit. So, a typical top off requirement of 1.25% would take at least 5 hours to stay within the maximum hourly guideline .
A longer time period is best. FWIW, I dose fully saturated limewater to equal the top off needs of my aquariums in 150 equal increments spread over 24 hours

[JDuong916]

How high does it get?

It gets to 8.5, thats when I throw a liter of soda water in and it drops .3 just like your article predicted. I used fully saturated kalk which was way more than my tank needed. After I adjust the saturation to my tank demands PH has stayed fairly constant.

Earlier you said if I were to add soda water directly to the kalk it would produce insoluble calcium carbonate. Why doesnt this happen when the saturated kalk water is added to the main tank? Wouldn't the lower PH cause the calcium carbonate to become insoluble as well?

[Randy Holmes-Farley]

Adding CO2 to limewater adds the CO2 --> carbonate needed for precipitation.

In the main tank the pH is far lower (8.2 vs 12.5) so most of the carbonte is actually present as bicarbonate, it is far more diluted, and there are other ions (magnesium, sodium, etc.) which also tend to inhibit precipitation of calcium carbonate.

[disc1]

lower pH increases the solubility of the calcium carbonate.

The soda water precipitates the kalk not because of the pH but because it makes carbonate. CO2 + H2O --> H2CO3 --> 2H+ + CO3--

It doesn't precipitate in the tank because the concentration is lower.

Here's the reader's digest on solubility...

There is a number called the "Solubility Product" for any given ionic compound. This number represents the maximum amount of something you can have dissolved.

It works like this, you multiply the concentration of calcium by the concentration of carbonate. The result cannot be greater than the solubility product or calcium carbonate will precipitate until you get back below it. Since it is the product of those two numbers it ends up working like a see-saw. You can have more calcium, but you can't then have as much alkalinity. Or you can have more alkalinity, but you then cannot have as much calcium. Those two can be at whatever levels they want, so long as the product of them multiplied together doesn't go over that SP number for calcium carbonate.


Now in the kalk bucket, the calcium concentration is really high. And so is the pH, that solubility product number is pH dependent and at high pH it is a much lower number. If you add soda water, you've added a high concentration of carbonate. If both calcium and carbonate are high, then multiplied together they'll be really high and be over the SP and you'll get precipitation.

Now when you pour a little kalk into the tank it gets diluted out to the tank volume. The calcium concentration isn't so high any more. So now you can afford to have some carbonate around without getting precipitation.

[dgelz]

If my levels are uncomfortably high, I just dilute the amount if kalk in my ato. Make thing easy. Considering all these supplements to lower ph seems unnecessary. Keep it simple.

[JDuong916]

If my levels are uncomfortably high, I just dilute the amount if kalk in my ato. Make thing easy. Considering all these supplements to lower ph seems unnecessary. Keep it simple.

That's what I did and its working great. I like simple.