PH below 6.5 kills bacteria? - The Planted Tank Forum
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post #1 of 42 (permalink) Old 09-07-2011, 12:50 PM Thread Starter
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PH below 6.5 kills bacteria?

I've recently read on the forum here that a ph below 6.5 will kill benefical bacteria in the filter, I was wondernig if this was true? I do not see how this can be true b/c discus buffers drop the ph to about 5 respectively and I've seen that other people will inject CO2 and have a ph below 6.5. My tapwater has a ph of about 7(maybe a lil lower) with a GH and KH of 3. My current set up I buffer the water to maintain a ph of 6.7 with 30ppm of CO2. I'm getting a new tank and do not want to buffer the water any more to avoid fluctuation of CO2 because of water changes. Normally ph has to drop a full degree to have acceptable CO2, if I inject CO2 into the new tank unbuffered it will put the ph I'm guessing right now somewhere in the range 5.8ish. Is this going to be a problem with bacteria in the filters doing its job?
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post #2 of 42 (permalink) Old 09-07-2011, 03:29 PM
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True, there are several reputable research papers saying that as pH drops below 6.5, nitrobacter and nitrosonomas (your biofilter) shut down then die.

And I do observe what appears to be a reduction in the bacterial colony in HOB filters that I use as CO2 diffusers.

But as you have observed, some people run this low without actual problems in real aquariums. Why this is, I don't think anyone knows for sure. In a planted tank, plants can take up the role of primary biofilter, especially with the added growth from CO2. In discus tanks, something else must be responsible; it could be that bacteria adapt over time, or another species we're not familiar with moves in.

But forget the statement about "pH has to drop a full degree to have acceptable CO2" entirely. pH is a logarithmic, not a linear scale. Every 1 point drop from 7.0 represents a tenfold increase in acidity, which makes this rule incorrect, and predicting your final value difficult.

Your tapwater's KH of 3 is plenty of buffering capacity to avoid a pH crash (a rapid, uncontrolled drop in pH, when the ratio of acidicity/alkalinity gets too far out of balance). Stop adding buffers, and you'll probably end up at 6.2-6.4, rather than 5.8. I've run at 6.2 without problems.

So I say go for it. But I would test ammonia levels and watch the tank after the change, just to make sure.
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post #3 of 42 (permalink) Old 09-07-2011, 04:41 PM Thread Starter
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Thanks for the info. I'm gonna give it a try, Everyone else is doing it lol
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post #4 of 42 (permalink) Old 09-07-2011, 05:16 PM
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so that mean all my good bacteria are dead now, because my PH read yellow (about 6.0) on API test kit, that is with co2 being dosed.

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post #5 of 42 (permalink) Old 09-07-2011, 07:00 PM
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**opinion alert** I would believe that the typical biofilter bacteria may die at a certain pH. However, as in most living systems there are other less efficient bacteria that probably fill some of the space. Combined with plants and the fact that the pH is not exactly the same everywhere you probably have some bacteria that grow as a film near the top of the aquarium.

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post #7 of 42 (permalink) Old 09-07-2011, 07:15 PM
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Your links were truncated and do not all work.

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post #8 of 42 (permalink) Old 09-07-2011, 07:15 PM
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Originally Posted by stewardwildcat View Post
**opinion alert** I would believe that the typical biofilter bacteria may die at a certain pH. However, as in most living systems there are other less efficient bacteria that probably fill some of the space. Combined with plants and the fact that the pH is not exactly the same everywhere you probably have some bacteria that grow as a film near the top of the aquarium.
You're probably right. After all, you can wipe out the normal flora for any system including those of the human body and another variety of bacteria will take that place but do they perform the same function as well? Are there interesting and undesirable side effects to being colonized by an opportunistic organism?
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post #9 of 42 (permalink) Old 09-07-2011, 07:24 PM
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Right, efficiency and bi products may be a problem outside of the "usual" Nitrification parameters.

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post #10 of 42 (permalink) Old 09-07-2011, 07:24 PM
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Your links were truncated and do not all work.
Fixed just for you .
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post #11 of 42 (permalink) Old 09-08-2011, 01:41 AM
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Gracias sir!

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post #12 of 42 (permalink) Old 09-08-2011, 01:47 AM
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to sum up most of those links. ph below 6.0 causes the bacteria to go into remission.. eventually they will die. however below 6.5 your bacterial efficiency is also about 30 % what it was compared to 7.0 fish don't die below 6 because the low ph converts the ammonia into a less toxic form. if u raised the ph they would all die. so its a trade off really. in the end plants will still become your final filter.. just depends on how you want the filtering done. i personally like nitrifying bacteria but there are plenty of people that run 5-6 ph tanks with no problems and are very happy with them

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post #13 of 42 (permalink) Old 09-08-2011, 01:52 AM
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I'd say they don't die completely, just their colonies become very small. I know in shrimpkeeping, especially in Asian countries, they keep the pH very low, between 5 and 6.5 and in order to maintain a good bio filter, they oxygenate the water and provide 5-10 times the bio filtration rated for their tank size.

IE. A 20 gallon tank would be running 3 canisters in a chain rated for a 30 gallon tank as well as 2 sponge filters rated for a 30 gallon tank, or a single sponge rated for a 40 gallon tank.

I myself am running one on tank, a canister rated for 40g, a canister rated for 20g, a sponge rated for a 40g, another sponge rated for a 20g, and a HOB breeder with some ceramic bio media in it.

But that's for shrimp in an unplanted tank, so it's probably quite a bit different from what you're looking into.
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post #14 of 42 (permalink) Old 09-08-2011, 02:57 AM
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People use lots of CO2 with high light tanks. That must necessarily drive the pH down almost always below 6.5. Those people find they have much less algae problems than if they don't use the CO2, and I would expect the opposite if the low pH was doing significant harm to nitrifying bacteria. Of course, it is always recommended to shut off the CO2 when the lights are off, which should be for about 14-16 hours a day, so any harm to the bacteria may be reversed during that time each day.

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post #15 of 42 (permalink) Old 09-08-2011, 03:24 AM
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People use lots of CO2 with high light tanks. That must necessarily drive the pH down almost always below 6.5. Those people find they have much less algae problems than if they don't use the CO2, and I would expect the opposite if the low pH was doing significant harm to nitrifying bacteria. Of course, it is always recommended to shut off the CO2 when the lights are off, which should be for about 14-16 hours a day, so any harm to the bacteria may be reversed during that time each day.

very true. the bacteria kinda of slows down and quickly comes back to full capacity. this is why well oxygenated tanks are KEY. to good fauna and flora health.

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