Low pH/KH, fish stress, what to do? - The Planted Tank Forum
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post #1 of 10 (permalink) Old 01-30-2009, 02:32 PM Thread Starter
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Low pH/KH, fish stress, what to do?

I have a (~5yr old) 37gal that has a DIY CO2(Hagen canister). Lately, I have been noticing a pH drop all the way from 7.2 to 6.2 over about 2 weeks. My KH is currently 3 deg and my drop checker is reading adequate CO2. My fish are looking very stressed as well.

I'm really concerned about this and would like to get the pH back to ~6.8/7 but I'm not sure how to go about this. Would raising the KH with baking soda help me out or am I way off base? Any help or suggestions would be greatly appreciated.
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post #2 of 10 (permalink) Old 01-30-2009, 03:30 PM
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I had the same problem from using RO water for water changes. With the injected CO2 it dropped my PH down to 6 and killed a bunch of my fish. I just did a few PWC with tap water and it came back up to 7. Obviously that depends on the acidity of your tap water.

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post #3 of 10 (permalink) Old 01-30-2009, 04:01 PM Thread Starter
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White the pH of my tap water is a lovely 7.6, the pH drop in my tank is persisting through PWC's.

I also began seeing this trend when I switched from Flourish Excel to DIY; so while my drop checker says the CO2 is normal, I'm concerned that it's high since my pH and KH are low.
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post #4 of 10 (permalink) Old 01-30-2009, 04:17 PM
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The pH drop from adding CO2 does not kill or otherwise distress fish. If you get too much CO2 and don't have enough water surface ripple to keep the tank O2 up, that will distress the fish, and can kill them. But, it isn't the pH that does the harm.

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post #5 of 10 (permalink) Old 01-30-2009, 06:36 PM
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Quote:
Originally Posted by Hoppy View Post
The pH drop from adding CO2 does not kill or otherwise distress fish. If you get too much CO2 and don't have enough water surface ripple to keep the tank O2 up, that will distress the fish, and can kill them. But, it isn't the pH that does the harm.
Agreed. When I converted my 40 gallon unplanted tank to a planted tank with pressurized c02 injection at 30 PPM, the PH nosedived from about 8.5 to 6.5, but none of the fish were effected.
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post #6 of 10 (permalink) Old 01-31-2009, 03:13 AM
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hmm

all you people seem to have high ph to begin with though. im starting OUT at around 6.5. what the heck is going to happen when MINE noise dives after my CO2 pressurized kit gets set up?
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post #7 of 10 (permalink) Old 01-31-2009, 05:15 AM
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all you people seem to have high ph to begin with though. im starting OUT at around 6.5. what the heck is going to happen when MINE noise dives after my CO2 pressurized kit gets set up?
If you leave the pH test kit in the box, and pretend you don't have it, nothing will happen. But, if you take the kit out and measure the pH, the results may scare you enough that you do something that will harm the fish, like suddenly adding a lot of bicarbonate of soda to the water. Or, more typically, you will reduce the CO2 bubble rate a lot, and have very little CO2 in the water, so you will have a chance to learn how to get rid of several different algae. At least it will be educational.
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post #8 of 10 (permalink) Old 02-01-2009, 05:56 AM
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I also thought CO2 rather than pH is the cause of fish stress.

However after doing a weekly 50% water change, my pH would drop from 6.8 to 5.7 within one day. My tap water is very soft. The effect was fish at the surface with rapid breathing.

I added KH buffer and within a few hours the hyperventilation subsided. No change to CO2 output.

Since then i always add a little KH up after water changes which seems to avoid this problem.

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post #9 of 10 (permalink) Old 02-04-2009, 06:29 PM
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Hi LAKA

Is does this just happen at water change? I wonder if it's got anything to do with the fact that the carbonates from the CO2 equilibrium will react with any Ca (and Mg) cations which precipitate as CaC03 (and increase acidity)? Adding KH will replace the carbonates and restore the PH?

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post #10 of 10 (permalink) Old 02-05-2009, 01:28 AM
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I've pondered many times why this is occurring. It's true that in non CO2 systems alkaline water has very little free floating CO2. Most exists as CO3--. In neutral water CO2 is in equilibrium with HCO3- and in acidic water most CO2 exists in its free state.

In CO2 enriched water i am not sure how relevant this is however.

What i notice is that after a 50% water change, many of my larger fish, ie. angelfish, hyperventilate at the surface within 2-3 hours. My smaller fish such as tetras and bristlenose are fine. My redtail shark starts flashing when pH drops below 6.0. It only takes 2-3 hrs for my pH to drop from 6.7 to <6.0. Tap water KH about 1. my pH has dropped to 5.6. Very acidic!

I feel this quick pH drop is bringing on these fish changes. By buffering the water, there is a smaller and gradual pH shift that my fish seem to appreciate. As stated CO2 rates remains the same as does water agitation.

If anyone has another explanation i'd be glad to hear it.

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