Agreed filter sounds big enough. Here are a few questions.
What is the ph? You need to use a fresh test kit and not dip strips, test at various times of the day at first. I assume it coud be crashing hence you trying to buffer, if the ph is going too low the bacteria will become dormant.
What is your Nitrate reading for tap water and for the tank, again do not use dip strips.
How do you clean the filter, i assume in old tank water and not under the tap?
How often do you do partial water changes and do you use a dechlorinator?
If you can answer these then we will build up a better picture.
What is the ph? You need to use a fresh test kit and not dip strips, test at various times of the day at first. I assume it coud be crashing hence you trying to buffer, if the ph is going too low the bacteria will become dormant.
What is your Nitrate reading for tap water and for the tank, again do not use dip strips.
How do you clean the filter, i assume in old tank water and not under the tap?
How often do you do partial water changes and do you use a dechlorinator?
If you can answer these then we will build up a better picture.
