# pH 6.5 Buffer Question?



## ray-the-pilot (May 14, 2008)

OK this may jog some chemistry minded people here!

Has any one ever tried a citric acid buffer? 

I’ve been beating myself up trying to get the pH of my aquarium to stabilize at 6.5. The problem is with a bad substrate that contains CaCO3. I’ve been adding mineral acids but they only have a short term effect on the pH and it eventually goes up. 

I also tried using CO2 to bring the pH down but it is a monumentally slow process because of the insolubility of CO2 in water.

I did a search of the possible buffers at 6.5 and found only two that were good candidates: carbonic acid and citric acid. You cannot make a stable carbonic acid buffer at 6.5 but a citric acid buffer is perfect at 6.5. Now here is a really interesting compound, citric acid. It will increase KH and decrease pH. The usual candidates for increasing KH (NaHCO3, MgCO3, etc) will increase pH. 

OK, the question again:

Has anyone tried citrate buffers?


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## hoppycalif (Apr 7, 2005)

Buffers are highly undesirable in a planted tank. Don't concern yourself with the pH of the water. CO2 is injected to help the plants to grow - it is just another fertilizer, not to drop the pH, which it does as a side effect.

CO2 is highly soluble in water. It is 100 times more soluble than oxygen or nitrogen (approximately).

Adding a buffer just increases the total dissolved solids content of the water and that can be detrimental to the fish, which pH between around 5 and 8 isn't.


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## ray-the-pilot (May 14, 2008)

Well, my goal is to keep discus in a natural setting including plants. Keeping plants is only a secondary condition.

I want the pH to be stable at 6.5. I don’t want to put in $500 worth of discus until I can get stable acid water conditions; however, I do have my background fish in place. 

Unfortunately, I started with bad substrate that was contaminated with limestone. The initial pH of my tank went to 8.2. I’ve been struggling with getting it down for a few months. OK I probably should dump the tank and throw out the substrate but my fish and plants are doing so well with all the attention they are getting that I can’t seem to go to that extreme. 

I want a stable pH of 6.5 before adding CO2 and no more than a 0.2 change after adding any CO2. 

CO2 is either soluble or not soluble depending on what you are talking about. Lots of CO2 will dissolve in water but it is not stable. The CO2 in water is in equilibrium with the CO2 in the atmosphere. Since there is relatively little CO2 in the atmosphere, CO2 dissipates into the atmosphere, causing the pH to go up. That is why bicarbonate is a lousy buffer at pH 6.5 even though it has a pKa of 6.4. 

In a natural system, there is a dynamic equilibrium established between plants and animals. Plants take in CO2 causing the pH to go up. Animals produce CO2 causing the pH to go down. The natural buffering capacity of the water keeps this from changing too much. In tropical rainforests, acid soil tannins are the buffer system. My thought about citric acid is that it can take the place of soil tannins. 

I’m not interested in growing a garden. I’m interested in maintaining a natural setting biotype. 

BTW, in nature, algae ≠ evil. It is part of the ecosystem. I expect to have some in my aquarium.


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## Edward (May 25, 2004)

ray-the-pilot said:


> I'm interested in maintaining a natural setting biotype.


Good plan, so why do you want stable pH of 6.5? No such thing as stable pH where Discus live, definitely not citric acid which is toxic to fish. There is tons of humic acid from all of the dead jungle vegetation and humus lowering pH far bellow levels CO2 as carbonic acid can, 5.65. For your information humic compound pH can go as low as 3.5 - 4.00 without harming fish and plants. Do we see dead fish in rainy seasons? No. Still, rainwater has no KH, no buffering, pH falls down and no casualties. In contrary these conditions trigger fish breeding because these conditions are the cleanest, the best. 

My advice, forget about KH, pH and chemicals. Get a TDS conductivity tester calibrated in micro Siemens µS and maintain water at the lowest level you can, 100 - 200 µS. Set your CO2 to a fixed bubble rate and forget about it. 

Any Discus pictures yet?

Edward


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## TortoiseBoy (Dec 30, 2004)

Hi Ray,
Is running peat moss in your filter an option? I tend to agree with Edward about varying pH not being that much of an issue, but I can see how you wouldn't want 8.2 for discus. Maybe peat would be an intermediate step?

TB


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## TWood (Dec 9, 2004)

ray-the-pilot said:


> OK I probably should dump the tank and throw out the substrate but my fish and plants are doing so well with all the attention they are getting that I can't seem to go to that extreme.


Dump it. You will be fighting this battle -forever- if you don't. You'll wear yourself out and end up hating the tank.

When you have an inert substrate, then let the water stabilize and look at what you have to work with. Adding buffers is almost always a bad idea because it puts you into the spin cycle where you'll continually be chasing the numbers up and down their range. Discus can adapt to a broad range, they just can't breed in water with high TDS.


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## ray-the-pilot (May 14, 2008)

TWood said:


> Discus can adapt to a broad range, they just can't breed in water with high TDS.


You are probably right about dumping the tank but as for discus fish; I'll follow the advice from Gwynbrook Farms Dicus Hatchery (They do this for a living) where I intend to buy my fish.

"All discus are tank raised in our hatchery. Water temperature is 82 degrees. pH is 6.0 - 6.5. Water hardness is 180 ppm. Before ordering our discus make sure your tank is properly cycled and that the pH of the water is between 6.2 - 6.5. Do not put discus in alkaline water(any pH above 7.0)."

http://www.discushatchery.com/discusprices.html

I'm not in any rush so playing with my tank is fun.


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## TWood (Dec 9, 2004)

Yeah, I remember running into the fanatic attitude in Discus breeders when I looked into them. Tell them you really can't be bothered with that beefheart stuff and you just want to feed dry food. They'll act like you want to abuse their fish. We have breeders here in central Texas that use tapwater that's pretty hard and high in pH. They also feed dry food.

BTW, there are two ways to 'do' Discus. The easiest, but most expensive, is to buy them already grown out. Then you can convert them to dry food (if they aren't already) and not fight the mess. I wanted to go this route and asked one of those 'boutique' breeders if he'd convert them to dry food for me. He went ballistic on me and refused to even sell me his precious fish. WTF?

The other way is to buy small fish and force feed them the beefheart recipes, assuming you want big fish. Discus will put on size rapidly up until they hit sexual maturity (a few months) and then stop growing much. So the trick is to get a lot of mass on them early. That can't be done in a planted tank because of the large amount of waste they will produce. Growing them out like that requires a bare bottom tank and LOTS of water changes. So if you go that route, plan for it.


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## ray-the-pilot (May 14, 2008)

TWood said:


> We have breeders here in central Texas that use tapwater that's pretty hard and high in pH. They also feed dry food.


Can you give me the names, phone #'s or e-mail addresses? I'd like to buy some of their fish.


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## TWood (Dec 9, 2004)

It's been too many years, looks like they've moved on. I did find these guys in your neck of the woods:

http://www.discusmadness.com/


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## ray-the-pilot (May 14, 2008)

TWood said:


> I did find these guys in your neck of the woods:
> 
> http://www.discusmadness.com/


Hey thanks. They are not saying anything that I haven't already heard about keeping discus but they are local and I can give them a call. Double thanks!
RTP


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