personal experience

Hey everyone how are you all? Anyways I know quite a few people who have fish that are aggressive towards each other or just simply mixed the wrong fish and then theres me who decided to mix central and south american cichlids (turned out to be a success however in alot of cases it wouldnt have)...

Does anyone have an effective way to tell the bioload of a tank? I am giving away some of my fish and would like to know how many I can still have in the tank.