[hal2001]

I currently have a 90g FOWLR and I hate the Crushed Coral substrate that I put in. I would like to put in sand instead. What is the best way to do this?

[Samper]

I made this mistake a long time ago with a small tank I had. What all is in this system fish wise?? Disturbing a CC bed that's been there for a while can cause a whole mess of problems.

[Samper]

Regardless I'll give you my thoughts and some others can chime in.
First I'd siphon out most of the water to a rubbermaid tub, remove all the fish and LR into that tub or two seperate ones would be better to keep lr from falling and hurting anything. Then with an almost empty tank scoop out all the CC then siphon out all the detritus and water that's left. Have a fresh batch of water mixed for a WC. Get whatever sand your using and have it rinsed thoroughly to minimize clouding. Put your sand in, aquascape your rocks then add whats left of your old water and fish to the tank slowly trying not to disturb the sand as much as possible. Then like doing a WC add the rest of the ASW that you've had mixing for a while. Turn on everything and give it time to settle. The problem you might see first are pumps blowing sand everywhere. You may have to adjust flow. The next thing may be some algae blooms from any losses you might have had due to exposing sponges or something to the air. The sand will have to establish itself and your tank may go through a small cycle also. Be adament about maintenance especially during the few weeks after you do this. Keep up with WC's, run carbon and keep the skimmer clean. Good luck.

[Samper]

It may even be better to leave your fish out until the tank has settled for a few hours.

[hal2001]

Thanks for the info. I think sand would look a lot nicer however I'm afraid to make the change and kill all my fish. Could I do the change in phases like pull out 1/3 of the CC and replace it with sand and so forth. Also, my LFS has offered to babysit my fish until I finish with the whole change.

[leebca]

You don't mention how 'crowded' your tank is, with decorations, live rock, etc. Will you have easy access to all the substrate?

Next, you don't mention how deep the current substrate is? The deeper it is, the more problems can arise with disturbing it.

Next you don't mention how long your system has been running.

You don't also mention:
1. the presence/absence of live rock; how much you have
2. how you have been keeping your substrate clean
3. how, if at all, the substrate has been mixed/churned/disturbed over time (worms, snails, etc.).

I think with additional information, it may be a little clearer to recommend a path forward to change out your substrate.