There's several hunderd species of catfish in the hobby only a very few eat enough algae to make any impression. Even those that do need a proper diet and cannot exist on algae alone.

Ask your uncle, probably the water is from a desalination plant and therefore about neutral ph and very soft. If that's true then you can keep just about anything with only a few small adjustments.

A simple tank, assuming you could get the bits and pieces of course could look something like this:
40-60cm wide, 30 deep, 30 high, that's about 15 gallons I think. Get a single T5 fixture onto that.
10 ember tetras for the middle water layer
7 pygmy cories for the bottom.

Use a coarse sand for the bottom, find a nice piece of driftwood and soak well so it sinks and loses the salt. Tie some java fern and anubias nanae onto it, plant around it with vallisneria, bacopa or even eloda at the back, Cryptocoryne wendtii or pogestemon helferi or Rotala rotundifolia (does require frequent pruning) in the foreground to soften up the transition to the wood a bit. Find a few pebbles that don't react when exposed to vinegar and place those where you like.

An alternative, get some wood and a few pebbles and just get amazonian frogbit.