If you put the fish into the new 20 gallon tank you should move the filter media across too so it will help keep the water cleaner. Unfortunately if you do move the filter media across it will transfer the algae across too.
It also depends on how long the filter was turned off when you first moved the old tank. If the filter was off for more than a couple of hours most of the bacteria is probably dead and you might as well start the 20 gallon with new filter media.
If you do use new filter media in the 20 gallon, then pick up a bottle of liquid filter bacteria from the pet shop. There are several brands available and the directions say to add them once a week or whatever, and they help get the filter going faster. I recommend double dosing them each day for the first week fish are in the tank then don't bother using it after that. If there's only a little bit left after the week of daily double dosing then you can pour the last bit in the tank to get rid of it.
Try to add the filter bacteria supplement to the tank near the filter intake.
-------------------------
When you get test kits, get liquid test kits rather than dry paper strip kits. Check the expiry date on the packet. Keep the test kit cool and dry, I kept mine in a plastic icecream bucket with lid in the bottom of the fridge.
*NB* Make sure children and animals can't get the test kits because they have toxic chemicals in them.
-------------------------
If you decide to keep the pink widow tetra, then you can get another tank for it later on and add 10 more of them so there is a nice group of them. In the mean time just keep all the fish together until the 20 gallon settles down,
It also depends on how long the filter was turned off when you first moved the old tank. If the filter was off for more than a couple of hours most of the bacteria is probably dead and you might as well start the 20 gallon with new filter media.
If you do use new filter media in the 20 gallon, then pick up a bottle of liquid filter bacteria from the pet shop. There are several brands available and the directions say to add them once a week or whatever, and they help get the filter going faster. I recommend double dosing them each day for the first week fish are in the tank then don't bother using it after that. If there's only a little bit left after the week of daily double dosing then you can pour the last bit in the tank to get rid of it.
Try to add the filter bacteria supplement to the tank near the filter intake.
-------------------------
When you get test kits, get liquid test kits rather than dry paper strip kits. Check the expiry date on the packet. Keep the test kit cool and dry, I kept mine in a plastic icecream bucket with lid in the bottom of the fridge.
*NB* Make sure children and animals can't get the test kits because they have toxic chemicals in them.
-------------------------
If you decide to keep the pink widow tetra, then you can get another tank for it later on and add 10 more of them so there is a nice group of them. In the mean time just keep all the fish together until the 20 gallon settles down,