I agree on at least 50% water changes. I have 4 tanks and change 75% every week in all of them.
In post #9 you mentioned that your hardness is increasing in your tank. This cannot happen as a result of normal biological processes. Form your photos it seems most likely that the culprit is your substrate releasing calcium into the water. The gravel look like it may contain limestone. Obviously I can't tell from a photo but the colour looks right. Just FWIW fish don't like bright lighting and white substrate is not usually recommended. In time it will also tend to become an algae trap.
If you do decide to keep the substrate (e.g. if you are specifically trying to make your water harder) it is even more important to do regular large water changes to keep the tank water stable. The gravel will continue leaching calcium and your hardness will keep increasing unless you "dilute" it.
In post #9 you mentioned that your hardness is increasing in your tank. This cannot happen as a result of normal biological processes. Form your photos it seems most likely that the culprit is your substrate releasing calcium into the water. The gravel look like it may contain limestone. Obviously I can't tell from a photo but the colour looks right. Just FWIW fish don't like bright lighting and white substrate is not usually recommended. In time it will also tend to become an algae trap.
If you do decide to keep the substrate (e.g. if you are specifically trying to make your water harder) it is even more important to do regular large water changes to keep the tank water stable. The gravel will continue leaching calcium and your hardness will keep increasing unless you "dilute" it.