[graveyardworm]

Is the bottled water listed as RO water on the label? If not then it may have impurities which are fine for you to drink and even give the water a pleasant taste, but are not good for your tank.

Chemi clean wont do anything for a sand bed which contains silicates, silicate sand is okay though and it is unlikely that silicates will leach from the sand and cause problems.

Sounds like the skimmer is working about as well as a seaclone does. There are modifications you'll find here on RC to help boost its performance.

I would suggest investing in an RO/DI unit. One of the cheaper improvemnets you can make for the health of your tank, and reduce the likelyhood of impurities causing nuisance algae problems.