Basically hot water + scrub is the way to go. Some people recommend a very mild dilution of bleach, but I don’t think its necessary if the hot water can get the job done for you. Just make sure the scrub you use has no soap or chemical in it. Glass is porous and the soap/chemical can seep into the pores and then later mix with the water once you place fish in the tank and kill them.

If there is a stuborrn mark that wont come off with hot water, try a 1:10 dilution of bleach to remove it.

Once the tank is clean, let it sit dry.

Transferring your 10 gallon will be easy. Bring over everything from the 10 gallon. This includes the filter, gravel, ornaments, heater, plants, even the tank water. And bring the fish of course. Then, add more gravel at the bottom if you need to, add more ornaments if you need to, more plants if you need to, you get the picture.

The reason for this is that your 10 gallon filter, plants, ornaments, and gravel all include countless beneficial bacteria, and bringing these over basically transfers your cycle into the new tank, so it really is necessary. Once everything is brought in fill the rest of the 40 gallon with clean, dechlorinated water.

It’s a good idea to not feed them for a day or two after moving. Let them get used to the new house. Besides, they’d be too busy exploring and could easily pass on the food. Also, keep a close eye on your water parameters for one week, and if possible let them stay in the dark so they aren’t as nervous or stressed.

If you have a new filter for the 40 gallon, you have two options:

- Run both the old and the new filter for a month on the 40 gallon
- Open the old filter, and transfer the bacteria colony (usually in a mesh bag with those ceramic cylinders) to the new filter

I used this method when I had to clean a REALLY dirty fish tank.
Put an old towel down on the bath and put the fish tank on top so as not to scratch the bath .
Put the shower on as hot as it goes and then using a old tooth brush scrub the corners use a sponge to scrub the rest rinse and then take it out .

You can use washing up liquid to clean it we did but if you do RINSE RINSE RINSE .
When you take it out dry it with and old towel and then… you guessed it rinse again
Take it out and dry it.

That should do .

Transferring the fish – When adding the fish to the tank take out the fish and but them in a bucket temporarily .

Transfer the stinky gravel to the 40 gal (it stinks really bad)

Then add any new gravel to the new fish tank. Top it up with as much old fish tank water as possible . Then add fresh water .

Filter – You probably are going to use a more powerful filter right ? well you will have to run both filters for about two weeks (the old one) so that when the new filter is establishing the old one will keep the ammonia etc down .

OK the fish – put them in a bag like the ones from the shop and float them for 20 mins every five adding water from the fish tank .

That should do