darksky
We are not trying to upset you regarding the size of your tank if you type in the sizes you just gave into the volume calculator it confirms that your tank holds 54 litres
http://www.tropicalfishcentre.co.uk/Calc.htm
i worked it to be a little less at 50 litres
but your fish add up to a total of 10 inches length and it gives coldwater at 7.5 inches maximum!
you can pick up bigger tanks online and in local trade it papers real cheap .
Ok The tank is all you have at the moment so lets do what we can for the time being.
(how much of a gap should there be at the top of the tank to the top of the water?)
Simple enough that it doesnt overflow ! ( is there a piece of glass like a ledge near the top of the tank aproxamatly 1 inch from the top? these are called braces and if yours has that then i would say fill to the underside of this!
(im waiting 24hrs before i put the fish into the new tank water)
If you use a airstone this is to alow the chlorine to escape! It saves the expence of tapwater addatives.......I use interpet tap safe on my tanks
(squeeze the sponge out of the filter )this advice i would say is if your changing filters and you squeeze the good bacteria from the old filter into the new filter!
if you have a filter then keep it as it is! No need to squeeze, then when you think the filter needs a clean you only clean it in old tank water. This is where i think you have read squeeze filter in tank water . When you do a water change dont just throw the old tank water away wash your filter in it then throw it away!
i would not use the glass beads in your tank......it would only benafit you as it looks prety not your fish! keep the bottom free of anything,that way you can see when the poo needs syphoning !.....also as your tank is so small syphon any uneaten food off the bottom of the tank after 10-15 minutes of feeding.
feed little and miss one day a week! do regular small waterchanges and keep your eyes open for a larger thank
hope this clears up a few things