Question:
i have an 80 litre tank. It has 8 cardinal tetras, several sword plants and spanish moss. An old bogwood and usual gravel compliment the picture. An external Ehiem 222 filter, 1 freshwater muscle and aeration unit keeps the tank flowing. I do a 15% water change at least every fortnightly. And I feed the fish usually once a day.

The problem is that, lately, the aquarium water is turning very alkaline. 7.5+ I do the PH test and find the water turning very blue.

I tested the tap water- its a soft neutral 7.

What is going on??? And how can I solve it.

BTW, I live in the Doncaster, Melbourne Australia area.

Answer: I have a 10 gal tank which drops pH between water changes, and a 29gal tank which increases pH between changes. My tap water is around 7.2 pH.

The 10 gal has more plant surface area than the 29 gal. The 10 gal has a small power filter, the 29 gal has a power filter+ cannister filter.

I would expect both tanks to get more acid between water changes, but have not tried to ascertain the cause of the difference.

The solution for both of my tanks is water changes. I do 50% weekly for the 10gal and 25% weekly for the 29 gal.