I've been changing 25% water every 2 days in the both tanks. Since the 40 was a new tank and wasn't cycled before. The seachem badges show 0.05. That's the tank I lost the family members. TBH - I had the Gem in its own 10 gal for 2 days, then moved him to the 40. I didn't like the water clarity in the 10g. The 20 gal was pre-cycled and all fish are looking better. It has 4 fish, including the PBT, who looks better. Just filter floss for both tanks.