[PEMfish]

Ok, no substrate is fine IF you have a good bio filter. This means alot of ceramic bio media. Second, if you go bare bottom, your fishes colors might not look as good. ( dark colors are best... ) And no decor is stressful to your fish, plants will just float around so a good 20lbs of rock from your LFS would be highly beneficial. It will curve aggression too. Also, the PH buffer won't help as much as hurt. It makes the PF flux like mad. Stop using it. Then test your PH after a few W/Cs ( don't do a W/C till your tank is cycled ) and find fish that live in your PH. ( Btw ( By the way ) W/C = water change. )
Testing weekly is important. But until your tank is cycled test once every other day. Test for; PH, GH, KH, Ammonia, Nitrite, & Nitrate. Other weekly maintenance would be siphoning gravel ( if you have it ), Cleaning glass ( IF need be ), and a 15% W/C.
Cycle; Your tank will have amonnia producing fish. Ammonia ( NH3 ) is toxic. Bacteria ( in your Bio filter ) will transform it into nitrite ( NO2 ) witch is also harmful, but not quite as. It will be further transformed into Nitrate ( NO3 ) with is yet, a little less toxic. Any one of these compounds is deadly in high concentrations. So cycling your tank means growing bacteria to get rid of deadly ammonia,,, You must do this before adding fish or there ammonia will build up and kill them. So every other day, test for ammonia, It will go way up, then back down as bacteria grows. Then test for Nitrite until it gos up then down. And the same for NO3. Now SLOWLY add fish. ( 5 inches total per week ) You can have 20 2" fish in there, such as Guppy's, Neons, Cherry barbs, and White clouds to name a few. But remember PH ( and GH, and KH ).
Can you tell me your exact filter please?