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Old 05-23-2005, 11:02 AM   #1
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Impossible (deadly) pH swing?!

I did a 20% 50/50 RO/tap water change last night and this morning I had three dead or nearly dead blue tetras, so I decided to test the water. It had a pH of 7.6+, so then I tested the water I added-7.4, so then I tested the water I had taken out-7.2! What Is going on here? The only other thing that I did was filter the water with cheese cloth (I tested a sample of it in the old water-7.2-no change), and replaced the filter media with an old piece that had been rinsed out. How can the pH in my tank be higher than the water I took out and the water I added?!

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Old 05-23-2005, 01:46 PM   #2
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sounds like CO2 gass escaping from the new water raising the ph.. try ageing your water change water in a container for 24 hours and then testing its PH.. what is the water hardness? the KH because this could be a factor.. if your KH is very low these PH swings are very common.. HTH
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Old 05-23-2005, 01:55 PM   #3
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That really does not sound like that much of a pH swing. .4 should not be enough to kill your fish, I'm sure my pH swings close to that much or more when I do a water change because I use straight tap water through a Python and all my fish do fine. I think you might have another problem in your tank.
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Old 05-23-2005, 02:43 PM   #4
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a .4 swing on pH can cause MAJOR stress in fish. from 7.2 - 7.6 that is considered, by some, a major pH swing. depending on the fish, it may be enough to cause death
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Old 05-23-2005, 02:47 PM   #5
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Let me understand - the pH in your tank currently is 7.6, but the water you removed and the water you added test lower? Meaning, you took water out of your tank and the pH dropped once it was out of the tank?
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Old 05-23-2005, 02:52 PM   #6
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Only my blue tetras were affected. Of four three died and the other is just fine (but lonely). Blame the Aquarium Gods I guess.
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Old 05-23-2005, 02:55 PM   #7
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Quote:
Originally Posted by SerLunchbox
a .4 swing on pH can cause MAJOR stress in fish. from 7.2 - 7.6 that is considered, by some, a major pH swing. depending on the fish, it may be enough to cause death
Should not be enough to kill all but the most sensitive of fish (rays, etc).

Why, and exactly when, did you add pH 7.4?
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Old 05-23-2005, 03:05 PM   #8
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Quote:
Originally Posted by Toirtis
Quote:
Originally Posted by SerLunchbox
a .4 swing on pH can cause MAJOR stress in fish. from 7.2 - 7.6 that is considered, by some, a major pH swing. depending on the fish, it may be enough to cause death
Should not be enough to kill all but the most sensitive of fish (rays, etc).

Why, and exactly when, did you add pH 7.4?
It is my understanding that the mixed water added measured 7.4 pH, is that right?
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Old 05-23-2005, 03:08 PM   #9
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Quote:
Originally Posted by TankGirl
It is my understanding that the mixed water added measured 7.4 pH, is that right?
If that is the case, then it should be nearly impossible for 7.4 water and 7.2 water mixing to achieve an overall pH of 7.6, especially immediately (or at least within 36 hours)....either the test results were wrong, or there is some other very significant factor working on pH here.
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Old 05-23-2005, 03:29 PM   #10
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how often do you do water changes? do you have a log of your maintanace?
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Old 05-23-2005, 04:14 PM   #11
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depending on the fish, it may be enough to cause death
Tetras?
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Old 05-23-2005, 04:21 PM   #12
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Some tetra's are not hardy fish and can be delicate to pH swings such as that.
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Old 05-23-2005, 04:24 PM   #13
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Quote:
Originally Posted by Fishyfanatic
Some tetra's are not hardy fish and can be delicate to pH swings such as that.
Very few, if any, would be killed by a swing under .75 unless the tetras were already compromised.
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Old 05-23-2005, 04:29 PM   #14
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Some tetra's are not hardy fish and can be delicate to pH swings such as that.
Are you going to argue with ever post I make from now on?
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Old 05-23-2005, 04:34 PM   #15
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That is why I am so perplexed. 7.2 + 7.4 = 7.6 I tested all three twice with two tests (high range and mid range) for a total of four tests on each water source. Water in tank was 7.6 Water I gravel vacced out in food grade plastic bucket 7.2 (found a swordtail baby in it just now) 50/50 water still in culinary water storage jug 7.4 Change was made last night 9pm MDT. Tests were done this morning 9am MDT after overnight death of three fish. Previous change was one week before.
Just retested aquarium water...7.2!
These little guys appeared perfectly healthy before the change and when they were introduced to the tank it was around 7.8 Unless they all choked on swordtail babies I have no other explanition for the deaths. Only new tankmates are 3 small praecox rainbows added after last water change. Only recent death was a carpet surfing danio.
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Old 05-23-2005, 04:41 PM   #16
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I think it is possible that your test kit could vary slightly in results, since these kits are not as accurate as we might hope. It could be out of date, or been exposed to high temps, etc. to render it unreliable. There could even be a variation in the drop size of the reagent causing slightly different results. The accurate test kits/meters are extremely expensive and not typically what we use, and the AP kits are a good guide but that's about it.

I would not make any changes in your routine, which seems reasonable (you did not forget dechlor in the tap component of your PWC mix, right?) based on the results of a test kit. You are right to investigate, however, in the instance of fish death following PWC.

I would suspect other causes for the fish deaths, even if it is the "mystery" deaths that occur from time to time.
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Old 05-23-2005, 04:43 PM   #17
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I would suspect other causes for the fish deaths, even if it is the "mystery" deaths that occur from time to time.
I agree.
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Old 05-23-2005, 04:44 PM   #18
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Quote:
Originally Posted by Apocalypse_Gold
Water I gravel vacced out in food grade plastic bucket 7.2
OK, your results there could well have been affected by suspended decomposing biological matter stirred up by the vacuuming.

Quote:
Just retested aquarium water...7.2!
OK, lest say that your actual aquarium water was 7.6 (before you touched it to siphon, etc), and you added 7.4 water....that could account for a drop of 1-2 points....combine that with some decomposing material in your tank (wood/plants/?) and/or off-gassing and/or loss of buffering could drop the pH anopther point or so over 12 hours....so it may not be all that mysterious after all.
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Old 05-23-2005, 04:45 PM   #19
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Tap water went through carbon stages of my r/o filter and it sat for 24 hours so no chlorine (I've tested this before). Thanks for all your help. Just their 'time' I guess.
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Old 05-23-2005, 05:04 PM   #20
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It seemed like it could have been Old Tank Syndrome to me..
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