switch substrates

empty the tank
turn it over, wash out the sand
put in the new gravel

It took me several hours of work to change over my substrate - I washed the new substrate first, then removed the fish and some water to a bucket. I scooped out the old gravel into a bucket, allowed the water in the tank to settle a bit and carefully placed in the flourite by the cupfull. When it was all in I let the water settle, planted the plants and then refilled the tank. I left it all for about half an hour with the filters on to clear up the dust before I put the fish back.
I suggest you give yourself lots of time if you've got a large tank, it's not an easy job.

does that mess with the cycling at all?

Are you using an undergravel filter? If so, this will completely disrupt the biological filtration. Your plan to add extra filters for a few weeks is a good one, it will really help.
After you've made the switch, feed lightly and keep an eye on the NH3 and NO2 levels for a while - if either become elevated you'll need to do water changes to bring them down, just as you would during a fishy cycle.

my main concern is what will happen since the bacteria lives in the gravel. if you remove all the gravel at once, wont it hurt the cycle?

Click to expand...

IF you are using an undergravel, you won't want sand, If you aren't, the majority of your bacteria lives in the filters not the substrate. Bacteria is limited by available oxygen supply. in tanks without ugf plates and circulation, there isn't much if any O2 below the top 1/4 inch or so of substrate. at best you may have a colony as deep as 3/4 inch.

So if you want to change your substrate, the largest part of your bacteria colony is not going to be harmed. yes you will lose some, but probably not even enough to create a mini cycle unless you are maxed out on stocking. Also bear in mind that some of you ammonia production in your current tank comes from the stuff in the substrate decomposing. This mulm will be largely removed, and the stuff that stays in the water column will retain whatever bacteria it has developed as well. I wouldn't wory a lot, just keep an eye on things for a day or two and feed lightly until you know things are stable.

As far as removing the substrate, If it were me I'd suck it out with a siphon. If you use a straight piece of hose instead of your gravel vac, it will siphon with enough speed to pull the gravel up in large quantities. this may constitue a couple of large volume water changes to finish the job, but your fish shouldn't mind and won't have to be removed until you are ready to add your sand in. then they won't have to be out of the tank for as long. your plants can float around in the tank while this is all in the works, and shouldn't be harmed beyond any normal transplant stress that they will have to go through anyhow.

I transfer gravel from one UGF to another this way whenever I set up a new tank. it is really easy to suck out a lot of gravel quickly with a hose.
Dave

I had sand in my tank when i had it in my room
and it was great, unfortunatly the heat and humidity
caused by the 100 gal of water in my room was giving
me heat rash's very painful the sand would also clog up my canister
filter alot more than the gravel would, not to bad though...By the way
it was beach sand that i was using very nice i rinsed it well with the hose before adding to the tank.. Well when I
moved the tanks outside onto the deck I dumped the sand and
went with gravel I had the fish in a bare tank and
had everything cycled though before I added the
gravel. I went with a natural style gravel with some plants looks good
and all the fishies made it .. I only kept the bacteria that was in the
canister filter.

I was wondering about this as well, currently I have about an inch of gravel, when doing a big water change could i just place the sand on top?