Did you lower your temp? You can use any small fan and aim it at your sump water.
Check your TDS in your RODI water, have you changed your DI Resin in two years? If not it's probably way past due.
What kind of kits are you testing with? Have they expired? Your phosphates shouldn't be reading undetectable. Most LFS will check your water prams for you free.
Did you get a CU crew when you restored the tank and added the 7 fish? If not it's time for hermits and snails. Purchase the types that eat algae as not all do.
Try the above and do 20% water change every 2 weeks. Clean off the slime and vacuum the sand bed before each water change.
Those poor fish need fed every day, just enough that they can eat in 2 minutes. Cut off your pumps so they get it all but please feed every day at the least. I have always fed twice a day, good pellets or a quality frozen food. If you feed the cheaper frozen cubes, thaw, drain and rinse off liquid gunk or it will cause algae.
Keep us updated, good luck!