Hello Peter,
now here the details of the float valves -system.
There are normal valves from toilets – they are not very small.
Example: ebay.de/itm/Geberit-Fuellventil-Impuls-380-Aufputz-Spuelkasten-240700001-/380471136045?_trksid=p2054897.l4275
Valves from other manufacturers will also work. The transparent plastic part of the valve controls the liquid level. It is the floating part- it is adjustable.
In my 12 liter tanks that also work.
Of course you need a little space at the top of the tanks to mount (zum einhängen)
The blue tube (Inlet pipe) you can cut / saw off. (max. 5 cm)
(there are also smaller valves to buy – but they are very expensive)
The brackets I build mostly from plexiglas.
The valves cost with fittings (connection) about 22 €.
Fresh water comes from another room via a pipe. You can also use a hose. a friend also fills his tank in the living room with one of these valves.
For the Paros / Bettas I use a 240 liter barrel with a normal garden pump. (Minimum pressure 1.5 bar) The water is prepared with leaves and alder cones. Peat is already in the individual tanks.
The inlet hoses are food safe.
The old water comes out with normal hoses. I use different attachments for the tanks. (Photo)
In my breeding room are everywhere drain tubes. In a living room you need a longer hose, of course.
Your reply: “As often as possible”
Yes, I am the same opinion.
When the water is well prepared / modified can not go wrong.
I change about 50% every week. More often in tanks with many young fish and large quantities of forage.