Hi
For the filter question i would ure a normal sponge cartridge filter and sit it just below the surface of the water this disturbs the top and does not unset the axolotl roaming about on the bottom.
I have a fluval 4 in my largest tank and it has a directional nozzle and power notch to pump the water faster or slower.
If u were to do without a filter ( i would not advise as they can be messy buggers) 10 % daily water chages with declorinated water.
You can buy declorinator from fish / pet shops cost about a ÂŁ5 and if u only have one tank it last for ages.
Im sure u know that gravel is a no no for axolotls as it can be impacted in its gut, Bare tank or play sand, I buy my sand from Argos.
Its about ÂŁ4 and all u have to do it stick it in a old pillow case and rinse it through about a dozen times till the water runs clear.
2 foot is minimum for one axolotl and additional foot for every extra axolotl u add.
But the more room the better.
Best food to feed Axolotls is earthworms, Its always best to oak them in warm water for ten mins, this allows them to release there defense toxins which makes the axolotl not spit the worm out once fed.
Other things i give them is bloodworms, prawns, pellets and on ocassion. :2thumb: