changing substrate in active tank

[meadeam]

I have a tank that has been up now for over 2 years.  I initially used bagged aquasoil capped with play sand.  I've let the plants get out of hand, and although the tank is healthy, it looks bad and I'm not happy with sand in the long run.   I'm afraid to make too many changes with the fish in, so I am thinking I should setup a temporary tank in a rubbermaid tote and move the fish and shrimp there while I work on the tank.  Alternatively, I could vaccum out the sand over a few days and slowly replace with the smooth gravel I intend to use.  Either way, i'd be pulling the plants out and re-planting.  Do you think I should set up the temporary tank for the plants and fish while I redo their tank, or try to do it with the fish in?  I'm not sure which is more effort, and/or better for the livestock.

I suppose a third option would be to very slowly make the changes over a period of weeks or months, doing only a little at a time so the tank isn't too upset all at once.  Once concern I have is releasing whatever lurks beneath the sand; I am afraid of some anaerobic nasties, or gasses that could be lurking down there.

[jwcarlson]

Yes, I would set up another tank or bucket and relocate them.  Bring over any filter and run it in the temporary setup to keep the bacteria going.  This way you can take your time and do it right instead of cutting a bunch of corners and possibly feeling rushed.  I wouldn't feed them in the temporary setup.

[meadeam]

I've been running a medium sponge filter in the tank for over a year alongside the external canister, so I have a filter to start the temporary tank with.  I'd also be floating the plants I intend to keep, so ideally they would bring some biofilter with them as well.   I've actually done this method before when I started this tank now that I am remembering, and it wasn't too bad.    

[beastie]

I did change substrate in a running tank twice, quite recently and it is always a mess, depending if you used root tabs in the substrate ( in that case keeping fish in there is a no go) and how large the tank is, cause the larger the tank, with a slower suction you have a good chance of taking out the substrate with the detritus too without causing too much destabilisation.

However, a temp cycled tank is an easier solution anyway: ) 

[meadeam]

I think I already knew the answer, I just needed to confirm it.  Thanks!

[meadeam]

As I consider taking on this project, I am now wondering if it is even neccessary.  The tank currently has mesh bagged aquasoil under an inch or so of sand.  I do need to replant several things, and probably add some more sand.  But prior to letting it get out of control, this tank was doing exceptionally well.  The main problem is I never trimmed the plants, and I let the floaters block all of the light, stunting everything below that couldn't cope with the lack of light.  The anubias and java ferns are doing ok, the bacopa simply reached for the stars and emerged in places, even flowering.  It's a very healthy tank in terms of water, needing very little in the way of water changes.  Maybe I don't want to disturb it.  It's been balanced and doing well in every way except aesthetically for a long time now.  I had the urge to redo it, but maybe some careful maintenance is all it needs.