I've recently been having some bad PH crashes... any idea on the cause?

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Carefree_Dude

Piranha
MFK Member
Feb 4, 2011
1,226
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81
Portland, OR
A few weeks ago I started having bad PH crashes. The water comes out of the tap at a PH of 7, but after a few days the test shows its at 6 (the lowest my test goes). Most of my fish dont' mind it, but its doing horrible things to the slime coat of one of my fish. I'm having to do a 70% water change every few days in order to "fix" the problem. Any idea what could be causing my PH drop? The only change I've done to the aquarium in the past several weeks is remove a bunch of plastic plants. Also, oddly enough, it's only affecting one of my aquariums.

I plan on getting some crushed coral to help buffer the PH in the tank. How much should I add? The tank is a 210 gallon.
 
have you been cleaning gunk out of your filters? Do you have canister filters that have been running a month or 2 without cleaning them out?
If not cleaning them out, they become nitrate sinks, and the metabolism of gunk build up can cause acidification.
Also how many fish, and what size fish? Overstocked? Has a fish died unnoticed in a corner somewhere?
Over fed?
these can all cause acidification, especially if the alkalinity of the tap water for water changes does not have a high buffering capacity.
I just accessed the Portland 2012 water quality report, and alkalinity was 6.5 to 16 (didn't specify what units were used) I'm guessing ppm. (where I live alkalinity out of the tap is between 90-100ppm. Your water hardness is just a bit below neutral.
This is due to source water, and the use of crushed coral seems to me, to be a good idea, it
can help the buffering, but is basically just a band-aid, and you will want to find the source, as opposed to just covering it up.
 
i have a 55 gallon aquarium as a sump filter. i clean the excess gunk out and rinse the filter media every two weeks (rinse in tank water). there usually isnt much gunk to remove.

i do have several large severums, geos, a very big fire eel, a big jade goby, a big black ghost knife, and a couple big ornate bichirs. ive had this stock for some time now, and have never had this issue in the past.
 
Sounds like those fish may have grown to a point that they may be just overwhelming the capacity of tank and sump to buffer the amount of waste they all constantly produce. That's quite a load for the amount of water.
 
I don't read the full posts so sorry if I'm repeating but did you add anything new to the tank recently? I added some rocks once and checked my ph the next day and it dropped hard.


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Without knowing the hardness of your water, measuring the pH is almost meaningless. When you've got a bit of time have a read of this article here to understand it better; http://www.tbas1.com/Exchange/The New England 11.pdf

If your water is very hard and has a high buffering capacity then a drop from pH 7 to 6 could represent a huge shift in water parameters. But if your water is soft with very little mineral content, the pH could shift from 7 to 6 and back again in a 24 hour period (from things like plants absorbing/releasing CO2 etc) and it wouldn't make a lick of difference to your fish. My water supply is rain water collected on our roof and stored in a large plastic tank, it is essentially RO water with virtually no dissolved solids (007PPM last time I checked), no hardness and a pH that is off-the-chart yellow. Despite this I can do a 40% water change on my tank with a pH of ~7 and it doesn't throw anything out of whack. Why? Because the pH of the new water, with it's complete lack of hardness/buffering capacity, adjusts very quickly to the minimal hardness I maintain in the tank. I have a bit of beach sand, which is about 95% crushed shell, mixed in with the regular sand to prevent the pH crashing (and I mean really crashing, like to <5!) because of the large quantity of driftwood I have. Because of the low hardness the pH can and will fluctuate by a reasonable amount without having any effect on the fish, so long as the extremes are avoided.

Before you start messing about with your water do yourself a favour and invest in some gear for measuring the hardness of your water, GH/KH test kits and if you like a TDS meter. If your water has only a low to moderate hardness I wouldn't be too worried about the drop in pH to 6.0, but you could always add a small quantity of shell/limestone/coral to the system to prevent it dropping too much. Just don't go too far the other way as the fish you're keeping do prefer water on the softer/more acidic side of neutral. If the water coming out of your tap is hard yet the pH is still dropping once added to the tank, then as duanes suggested there may be other causes behind the dropping pH.
 
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