Hi, I'm new to keeping fish. I have a 230litre tank I have had it for 4 months now, I get confused understanding what my stock limit is. I have an external filter with 2kg biohome media and a sponge air filter.
Stocking limit is based on a wide range of things like water changes, amount of food going into the tank, how peaceful or aggressive the inhabitants are, their size and swimming space requirements.
In a 4ft tank like yours, you could have 200 neon tetras (about 200 inches of fish) and that would be fine, but if you tried to put a 12 inch Jack Dempsey cichlid and a 12 inch Black belt cichlid in the tank, it would end badly due to the aggressive nature of these two cichlids. But the neons would be fine because they are peaceful and normally live in large groups.
If you feed your fish 10 times a day and do a water change once a month, then your tank is overstocked. If you feed twice a week and do a 75% water change every couple of days, you could add more fish.
So there are lots of variables, but I would say your tank is not currently overstocked if you feed once or twice a day, and do a 75% water change and gravel clean the substrate once a week.
It also depends on how big your crayfish are?
We have marron (freshwater crayfish) in Western Australia and they grow to about 18-24inches long. I'm assuming the blue crayfish you have are much smaller (around 4-6 inches long).
You will have to watch the angelfish when they mature. If two of them pair off, they will pick on the third angelfish and it will need to be removed.