My comments are general, as I've no idea from this thread what is in the tank or its size, etc.
Keeping the water "OK," whatever one may mean by this, is only pone part of the issue. If an aquarium is over-stocked, the fish in it are being subjected to stress continually 24/7 and this will take its toll at some point; usually it is a cumulative process, bu which I mean that health issues increase [they may not be obvious externally], aggression (or the opposite) may increase, up to the point at which the fish will die prematurely. There is no way around this, except to remove fish or set up a properly-sized tank for the species.
More frequent water changes can "help" but not solve the problem in all cases. The individual behaviours and needs of the fish species cannot be altered, they are programmed into the fish by natural evolution. So, space requirements will remain difficult regardless of water changes. Where more frequent water changes help is by reducing the "crud" [urine, pheromones, allomones, dissolved solid wastes, etc] that naturally and steadily increases in any enclosed space with fish. The more fish, or the larger the fish, the faster the water deteriorates. More water changes reduce this detriment, but the physical space is still an issue that water changes can't solve.