Hi Everyone,

I have a very wierd problem. Two days ago my ph was stable as it always is at 8.20-8.25. Yesterday I checked the tank and it was at 8.33. I then checked it today and it is at 8.15-8.16. I did a water change last saturday which I have been doing for about 3 years every two weeks of 25%. This is a fish only tank with live rock. I was wondering do A/C's cause any problems in tanks such as high co2 levels Since that is the only thing that has changed. I change my water with RO/DI and use IO, I then use Kent Marine buffer on day 1 and 2 after water changes to level ph from 8.0 to 8.2-8.25. I will check my nitrates and nitrite tommorow but dont believe they are high. Below is a list of my normal level will check them tommorow. I use a PH meter and confirmed the readings with test kits.

Temp 79 - 80
PH 8.25 (usually now 8.16 today 8.33 yesterday?)
Alk 3.5 - 4
Calcium 380 - 400
Nitrate 0
Nitrite 0
Ammonia 0

What could cause this rise then fall. I have two puffer fish in the tank and live rock. I use a fluval 304 which I clean every two weeks and a emperor pengiun which I clean on the other 2 weeks. I also have a Remora Pro with Mag3 and 1 maxijet 1200 and a 301 with filter/carbon which I replace when I replace or clean the emperor pengiun on alternating 2 weeks.

Thank You