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Thread: Big PH Spike in Cycling Tank

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    Registered Member lastflea's Avatar
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    Default Big PH Spike in Cycling Tank

    Hi everyone.

    Started my cycle yesterday by adding 4ppm ammonia to my tank. Filtration wise I have a large sponge filter, and some sponge in the first chamber of my sump. My PH, in the tank, before adding ammonia was 7.4, and today it's 8.4. Obviously still early days yet, with 0 nitrites, but I'm very curious to know if this is normal. So far all I can find is that ammonia can cause a crash, not a spike. Would it be more to do with the sponge filter aerating the water?

    Rob

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    Default Re: Big PH Spike in Cycling Tank

    Hi Rob. Your water probably has a large upward pH swing because of excess dissolved CO2, where it comes out of the tap at a lower pH and then with aeration it goes up to over 8. Its important to know what your water's pH does as it ages. Measure the pH straight from the tap, then aerate some in a bucket for a day and measure again. If the pH goes way up then you will want to age your water for doing large water changes, or the sudden shift during WCs will cause stress.

    The other part of this is that hardware store ammonia, when you first add a large amount, causes a temporary spike in pH that lasts a couple of hours, then settles with a slightly higher pH than where it started. If the two pH measurements of 7.4 and 8.4 were more than about 6 hours apart, it wouldn't be from the ammonia, more likely a pH swing from excess CO2.

    When you read things about ammonia causing a pH crash, that isn't the ammonia, its the consumption of ammonia by nitrifying bacteria in a cycled filter, a slower process that reduces the buffer (KH) and adds acid to the water. That won't be a problem with your water.

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    Registered Member lastflea's Avatar
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    Default Re: Big PH Spike in Cycling Tank

    Hi Dan, thanks for your reply. My pH is 7.4 out the tap. I've had it in my tank a couple days before adding the sponge filter and ammonia yesterday. So basically the cause of the spike is the aeration from the filter? I've checked the pH today and it's dropped to 8.2, and this is over a 24hr period. My understanding is ageing water takes between 12 and 24hrs for the pH to settle down, so is this as low as it'll get? If so, perhaps my pH is a tad high for discus, and will need to use a different method of filtration, if that's to blame. I kept fish a few years ago, and didn't have this problem with water changes, and didn't use filter sponges or air stones.

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    Default Re: Big PH Spike in Cycling Tank

    It isn't the type of filtration, its the aeration/circulation. The water has extra CO2 while under pressure, which lowers the pH, and with aeration or circulation the excess CO2 leaves the water until the concentration of CO2 reaches an equilibrium with atmospheric CO2. So after 12-24 hours the pH settles and becomes more or less constant, in your case around 8.2 apparently. You will see the pH swing up like this in an ageing barrel, or in the tank.

    If your pH really does swing from 7.4 up to 8.2, you would be limited to the smaller WCs of 25-30% or so that are typical with most fish tanks, but with discus, especially juveniles, you really need to be able to do much larger WCs for good health and growth, which is why many age their water first in a barrel. It wouldn't hurt to do the bucket test with an airstone, to verify the pH swing independent of other factors like the ammonia, sand, gravel, decor etc.

    On the forum I have seen where a lot of people have good success with domestic discus in a higher pH. The main thing is plenty of clean water, aged if necessary. You can do well with a wide range of pH, you just don't want to have the sudden downward shift in pH during water changes.

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    Registered Member lastflea's Avatar
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    Default Re: Big PH Spike in Cycling Tank

    Yes, it makes sense to test the water without the ammonia. My tank is bare, so there's no other factors to consider. The water has been passing through a sump for two days (second hand tank so checking for leaks), prior to starting the cycle and was 7.4. If air pumps are used to aerate the water, then the sponge filter must be the cause of the spike? I'll age a bucket with an air pump tomorrow for 24hrs and see how that turns out. Thanks again

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