Ph Swing.. limit? - The Planted Tank Forum
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post #1 of 4 (permalink) Old 03-26-2009, 02:44 AM Thread Starter
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Ph Swing.. limit?

0.5, 0.2?

what is considered harmful and deadly to fish?
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post #2 of 4 (permalink) Old 03-26-2009, 03:47 AM
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Over what period of time and what kind of fish?

IMO, the risk of pH swings alone is a bit overrated.
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post #3 of 4 (permalink) Old 03-26-2009, 06:06 AM
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I have read, in the past, that pH swings caused by changes in carbonate hardness (kH) affect fish more than pH swings caused by the addition/removal of acids. Therefore, adding or removing CO2 (carbonic acid in the tank) is less of an issue than, say, suddenly adding significant amounts of calcium carbonate, or sodium bicarbonate (which affects the kH).

In my personal experience, my fish have endured occasional pH swings between 6.5 and 7.5 with no harm. The swing is due to CO2 de-gassing when doing maintenance. On a daily basis, however, the swing is always between 6.4-6.5 using a pH controller. All my fish (zebra danios and tiger barbs) are more than six years old with no diseases, they have great colors, and general vibrancy. But since I always prepare my own aquarium water using RO water as the foundation, I design the kH to always be around 7 degrees (125ppm as CaCO3).

So, in my case, the kH has been fairly constant for years, while the pH due to CO2 content has been all over the place (pH 6.0-8.0).


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post #4 of 4 (permalink) Old 03-26-2009, 04:02 PM
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My experience is that my fish enjoy big water changes. I have done two consecutive 75% changes just an hour apart, with the fish reacting very favorably to that. I use only tap water, straight from the tap, a mix of hot and cold water to get close to the right temperature. I use Prime to dechlorinate the water as I add it.

This changes the pH considerably in the tank, and does it pretty quickly, since I have high CO2 concentration in the tank, and the tap will have a lower concentration. Also, I never measure KH, but my water supply is normally river water, with low KH, also contributing to a big pH swing as I do water changes.

I also shut off the CO2 when the lights are off. So the pH will increase throughout the night as the CO2 escapes from the water. Then, when the lights come on, the CO2 comes back on, to again lower the pH. No problem for my fish.

I think the consensus today is that pH is not a concern for fish, either big changes in pH or the actual pH. In fact pH is just a result of other factors, not an independent parameter at all.

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