You need to check you CO2 level but I VERY much doubt that a DIY system has got a 70G tank to 10PPM, never mind the "recommended" 30PPM. DIY CO2 usually falls by the wayside at about 30USFG. It is very unlikely that the CO2 is the stresser for your SAE. I would be looking for other reasons. Tank mates, water parametres, temperature, water circulation rate, etc.
I just reread your post. You have more than 1 SAE in that size tank? That is likely the issue right there.
Vic