If this is a new tank, it could be diatoms. If so, add a cleanup crew if you havent already. Fighting conch, nass. snails and cerith snails seem to work with the sand bed a little better than other snails. With the water, yes switch before other algeas start that are harder to maintain. If an ro/di unit is out of the question (like for myself) you could try asking your LFS if they will let you fill your containers (mine will for free) or go to walmart and buy their brand distilled water for now, I have been doing both for a few years. HTH