I have a 2.5 picotope. I upgraded the lighting with NO florescent (should have gone PC). For filtration I use the stock filter to run carbon and I converted an AC70 into a fuge(best improvement). There is quite a bit of evaporation. I do 50% water changes every week. There is an HOB filter that hides the heater by tetra I think. I would go that route. I had an auto top off for a while, but moved it to another tank. The corals seemed happiest with the ATO because there weren't any salinity swings. They also improved when I added a heater. Best of luck. I recommend a shrimp/goby combo or harlequin shrimp.