Changing Substrate

I took my fish out to change to sand, though I did my 125 litre when I had to empty it anyway to move it across the room.
I put the fish into a dustbin (~60 litres) which I keep just for fish things together with as much water as would fit. The heater and filter went in there too, switched on. The container needs to be covered, if it doesn't have a lid something like a towel will do. It stops the fish getting too stressed and stops them jumping out. My gravel was quite small so I could siphon it out. With larger gravel you'll have to use a scoop of some sort. The last few inches of water will be unusable as they'll be full of muck.

Then add your new substrate and some dechlorinated warm water. If using a bucket to refill you need to be careful not to disturb the sand. Some people put a plate on the sand and pour the water on top of that. I have a large yoghurt pot with a lot of holes punched in the bottom with a knitting needle which I use as a colander - a real colander was too big and unwieldy for me to manage. Once there is enough water for the fish to swim comfortably in, net them out of the container and add the old tank water then the heater, filter and decor. Top up with new water.

If you have real plants you'll need a bucket of tank  water for them and also for the decor as that will have a fair amount of bacteria on. With live plants, they need to go in at whichever stage you would normally plant them. Since mine are all attached to decor, I don't know when would be best.

Feed the fish lightly for a few days before and after, and monitor the ammonia and nitrite levels for several days. You will lose the bacteria on the grave but the loss should be made up quickly.

In my 180 and 50 litre tanks I have some fairly cheap sand that is sold at an LFS. It is beigey with larger dark bits. The betta's tank has Unipac silica sand which I wouldn't recommend on cost grounds - you'd need a lot for a 180 litre tank.
Some people use play sand of the type sold at Argos and B&Q though others say it is too fine grained and compacts too much. Americans often use pool filter sand (I think there are more people with swimming pools over there).

There is just so much choice when it comes to sand, and especially colour. Ultimately it comes down to which colour you prefer and how much you are prepared to pay.
But be careful with some of the 'fancy' sands as some of them could be dyed limestone and will alter the pH and hardness. I once bought some Unipac limpopo sand which is a dark gray and that failed the vinegar test. But I have read that the bags now on sale don't.

My sand isn't very deep because I don't have plants rooted in it.
The first 5kg bag did the 125 litre and the 50 litre. When I got the 180, I used a whole 5kg bag plus the sand from the 125, which would have been less than I put in there as some is lost at every water change. A couple of months ago I added about a third of another 5gk bag; I'd had enough of getting frozen washing it by the time I'd done that third. I'll add the rest when the weather gets warmer.
My 180 has a 42 x 18 inch footprint and the sand is maybe half an inch deep. So 5kg + ~2.5kg + 1.5ish kg = 9kg to give half an inch deep in that sized tank.

Don't forget you'll need to top up  every so often as you will lose some with water changes. If there is a lot in the bucket, if that's what you use, just wash it in tap water and put it back in the tank. The chlorine in that tiny amount of rinse water will do no harm.

Sorry Diz, hijacking your thread!!

 How easy is it to clean the sand. Does the fish poo get stuck to it? Does the sand cause a build up of gas (with buried poo)

I am going to transfer my current bacteria gravel + new washed when I set up the 60cm but I fancied a little spit of sand as a change.
I also have Tetra substrate which will stay where the gravel will be because that's where the plants will be

Hi Sue, do you mean, then, that you shouldn't Hoover the sand if you have live plants, or that you shouldn't Hoover if you have sand, live plants and fish that like to dig? Sorry, I know I'm being pedantic, but just wanted to be sure.

Thanks again Sue, that's very clear now. I don't think I want the sand to be too deep, just enough to hide the soil really

Hmm, maybe a thicker layer then. One last question, using the soil ( or I may go for the tropica plant substrate underneath sand) won't leach anything nasty into the water will it? Ideally, you'd do all this at the start of a fish less cycle, but since my fish will be going straight back in I thought I'd just check

Ok, Thanks Sue for all your patience.
Hopefully Richard will see this and share his expertise

I'd hate to be too definitive on this as I don't want to be blamed if you have problems 

I set up and planted my tanks a long time before adding fish and so don't have any experience of putting fish into a newly set up tank. However, Diana Walstad states that she adds her fish the same day or next day to her tanks with soil under sand/.gravel and obviously doesn't have problems.

If there is anything "nasty" in the soil that will leach into the water then you shouldn't be using that soil!

Water parameters can be unstable for a while after using soil. This might be, for example, if the pH of the soil is significantly different from your water. I'd advise plenty of testing, particularly of pH, and more frequent water changes than normal for the first couple of weeks. It should settle down by then, if not before. I'd avoid any soil that has a lot of organic matter as it will break down over time and increase instability. That's why the common type of potting compost is useless as it is largely organic.

My tanks with ordinary garden soil under an inch or so of either sand or fine gravel have now all been set up for 18 months or more and I've never had any problems whatsoever in spite of my relatively infrequent water changes and neglect of substrate vacuuming. Were it not physiologically impossible I'd say that my fish don't poo as I never see any sign of it