At the moment running set with undergravel filter and a skimmer but want to change to reef setup. This means getting rid of undergavel filter. I only have one tank. Can I change this setup gradully, syphoning off and then use r/o water to topup......removing live sand a bit at a time then take out the filter. Don't want to have to cycle tank again. It's a 30 gallon tank and about the same in live rock. And can this be done with my fish still in tank or is this idea a no no.