I am new to discus and heard that bare tank with only few pebbles are easier to clean rather than thick gravel.It is true? I plan to set up a 4 feet or 120cm x 45cm x 45cm tank.How many discus can i keep? How often and how many % of water I need to change regularly?
There is no fix rule how much water to be changed.
As long as the water should be kept clean.
If you overfeed them the water is dirty, you have to change water 50% to 100%.
As long as they live happily, there is no fix rule for number of fish in one tank.
You do not only count on number, you should consider the size too.
20 two inch fish and 20 adult fish means a lot of difference.
Aeration will also help.