Why would pH drop?

C

Corn-Picker

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Dec 30, 2003
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My tank has been up a few months. The water has been pretty steady at a pH of 8.2. I did a 5 gallon water change (30 gallon tank) last night, and when I checked the pH this morning, 7.8 :confused: This is especially confusing to me because I have 70 pounds (about 5 inches) of aragonite sand in the bottom of the tank.

What could cause this behavior?

Water Temp is 76
SG is 1.021
Ammonia is 0
Nitrite is 0.1 ppm
Nitrate is 0-5 ppm
 
The sand will help a bit, but no calcareous substrate will maintain a pH above 7.9. I can dredge up references if people want them. Proper pH depends on the buffers in your water.

First, do you always measure in the morning? It will be lowest at that point, when all of the photosynthetic organisms have been consuming O2 and generating CO2 in the dark.
Second, what is your alkalinity? Low alkalinity will indicate that the buffers in your system are depleted.

pH drops usually result from 2 problems.
1. Too much CO2, from too little circulation, too much metabolic activity, or too much CO2 in the room. This can be tested by vigorously aerating a sample. If the pH doesn't change, that's not the problem. If this is the problem, try adding another powerhead.
2. Organic acids, generated by waste. This will show up as a drop in alkalinity. Another water change, and maybe some debris removal might help.
 
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