Established 40 gal tank with water tested several times a week with the API liquid kit and 50% water change a week. Mix of plastic and live plant.

There have been no additions for quite some time and the stock is

5 ghost catfish
5 danio
10 neon tetra
2 red wag platy
3 balloon belly molly

The 10 year is asking if we can add any additional fish. Bottom feeder, guppies? I think we are near the responsible limit but am not sure.

A lot of stocking depends on how much filtration you have going on the tank. There is a bit more forgiveness if there is more than adequate filtration, and many here will reccomend having double the filtration for your tank size, in your case--80 gallons of filtration. A site to use (but is far from being the rule) is aqadvisor.com

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I should have mentioned I do run 2 filters. It is not double but not far from it.

Replace the plastics with 100% real and add more plants. I think you are getting close to where I would stop, but adding plants "can" allow you more adding room with less impact.