Welcome back to the forum and the hobby
Can you drop the filter cartridge and use sponge from a different brand of filter?
Sponges last for years and only need replacing when they fall apart. Cartridges are gimmicks to make you keep giving your money to a company.
Get a couple of 5 gallon buckets (food safe if possible) and use a permanent market to write "Fish only" on them. Use those specifically for the fish and nothing else.
Get a basic model gravel cleaner to gravel clean the substrate and syphon water out.
Maybe some frozen food to vary the fish's diet.
Did you want to try live plants instead of plastic?
If yes I can post a thing about basic plant care.
What is the GH
(general hardness), KH
(carbonate hardness) and pH of your water supply?
This information can usually be obtained from your water supply company's website or by telephoning them. If they can't help you, take a glass full of tap water to the local pet shop and get them to test it for you. Write the results down (in numbers) when they do the tests. And ask them what the results are in (eg: ppm
, dGH, or something else).
Depending on what the GH
of your water is, will determine what fish you should keep.
Angelfish, discus, most tetras, most barbs, Bettas, gouramis, rasbora, Corydoras and small species of suckermouth catfish all occur in soft water (GH
below 150ppm) and a pH below 7.0.
Livebearers (guppies, platies, swordtails, mollies), rainbowfish and goldfish occur in medium hard water with a GH
around 200-250ppm and a pH above 7.0.
If you have very hard water (GH
above 300ppm) then look at African Rift Lake cichlids, or use distilled or reverse osmosis water to reduce the GH
and keep fishes from softer water.