Also; 10 fish is a lot for a new tank! How new is the tank?
Small fish are going to be better than large ones, but you ought to be careful as it sounds like you may be justifying it for yourself. That is the behavior that leads to at least 90% of the tank crashes I’ve consulted on, so it’s good to exercise caution when assessing your own decisions. You also need to consider the species of fish not just the size. You mentioned you have Anthias. Anthias may be small, but they have a high bio-load equivalent to a large (or very large) fish. Just something to consider.
3 cubes a day is also a lot for 10 small fish. Even 10 small Anthias. But I’m glad to see you’re doing regular water changes to compensate! Great job making a schedule!
Seeing a pH drop when taking the skimmer offline is the first sign of a potentially overstocked tank. Basically, fish and corals are breathing a lot of CO2 into the water, and you’re decreasing the surface area between air and water. So the excess CO2 diffuses into the air at a slower rate, causing your tank to become more acidic. If you want to take the skimmer offline, you can help your pH by either 1) increasing surface agitation of your water by aiming a pump upwards, 2) adding a refugium with algae, and/or 3) adding some houseplants around your tank. Small changes can have cumulative effects.
Note: Its better to think of the stocking capacity of a tank is a fluid number. Yours may be overstocked because of its age. But once again, I don’t have enough info yet to provide specific advice.
