Hi Shrimper, I was actually addressing the "Check the threads below" comment to f1sh. but I appreciate your response. Those are both reasonable methods in, as Inchworm says, a cycled tank. I have actually changed the substrate in many tanks and added sand to quite a few. I don't remember ever losing any fish in the process--except perhaps in moving, which is a whole other dilema. I don't give my method because it is not the more "recommended" way. I use the "rip the bandade off and be done with it" method.
I just added several small buckets of sand to the Brochis multiradiatus tank. All I did was make sure that the sand was well rinsed, which with play sand is not hard when done a bit at a time. It is already fairly clean. Then I turned the filter off, and poured sand from the submerged bucket into the opposite end of the tank from where I feed them. I kept them shooed away as they were curious. There was no big dust storm and the tank was settled immediately. I turned the tank light off and gave them time to settle in. An hour later I turned the filter back on. I frequently turn the filters off or down for brief periods to feed.
I also changed substrate awhile back, because I had mistakenly put high PH/marine sand in. I did not want to fool around and don't have lots of spare time. I again turned the filter off, removed the decore--which really freaks the fish out--and shoveled the substrate out. Then I vacumed the tank bottom to remove as much of the coral as I could, and bucketed the new rinsed sand back in. I did not lose any fish. Of course they were upset, but no matter how I did it it would upset them, I figure. In this instance there was lots of calcium dust from the removed sand.
I assume I will get some back handed and impatient remarks or something, but that's what I do. It works for me. I do not recommend it since it is not the orthodox method. I was a little stressed last night and had just been accused of "kissing ass," which really isn't my style. I usually get in trouble for saying what I think.
I assume the person was projecting their own motives on me.
Anyway, if it felt that I was abrupt, I do appologize.