I have had a rotifer culture going for about a month or so. During this time the bottom has become nasty with a brown slime. So yesterday I carefully took out about 2 quarts of culture water and rotifers leaving the nasty water behind. I then made up 2 quarts of fresh saltwater. After dumping out the nasty old water and cleaning the aquarium, I added the clean 2 quarts of old culture and the fesh 2 quarts of saltwater to the now clean aquarium. Now my question is did I do this ok. The reason I ask is because I have heard to use old tank water microwaved and sterile instead of fresh saltwater. This morning I checked the culture and they seem to do great. Whats your thoughts. Thanks