water parameter question

[thartley]

I just tested the pH, ammonia, nitrite and gH levels of two tanks. One is a 20 gallon planted tank with only four small guppies. The other is a 10 gallon with a few floating plants with about a dozen guppies or so. Here are the readings:

20 gal:
0.025 or less ammonia
0.0 nitrite
7.6 pH
3 gH

10 gal:
0.0 ammonia
0.0 nitrite
7.6 pH
1 or less gH

The question is, why would the 10 gal. tank have zero gH (it changed to yellow on the first drop,) when the other has three gH if they both are using the same tap water?

There are no additional products being added to either tank to increase the hardness. No additional CO2 either. The 20 gal. tank may not be fully cycled yet. (I think I'll pick up a nitrate test kit today.) The 10 gal. is running an undergravel filter and a bio-wheel because we want to remove the UGF to convert to rooted plants.

Another question has to do with the pH. When I first started testing the pH a few weeks ago on the 20 gal., I was at 7.0. The last week it jumped up to 7.6. What would cause the jump? I have been doing a 20% partial water change about once a week. The last change was on Thursday.

Thanks,

[thartley]

I figured out why the pH has gone up in the tank. It has nothing to do with the conditions of the tank. I just tested my tap water and its pH is 7.6. So the partial water changes explains the change in the value over the last three weeks.

You can only obtain an accurate tap water pH if you let the water rest for at least 12 hours. 24 hours is better.