
yes its fine, imagine a big siphon coming into your house and sucking up all the dirt LOL
You can test straight away, what are you testing for?

your filter only needs maintenance once or twice a month, unless you notice it getting weaker. if its getting weaker its usually because its getting clogged. when you 'clean it' just rinse the sponges/media in old tank water. dont be too vigorous, just enough to get the loose dirt off, then put it back together.
How much water conditioner should I have used. I used 4 drops in the 20% water I put back in. Is that right or am I suppossed to add for the whole tank?