Domestic Filter on a fish tanks

[Nato]

Hi.
A friend of mine showev me a setup he has in his backyard that carried two standard water filters used in houses.
The filters had the concrete tank crystal clear.
He boasted he cleans the filter every two to three weeks and he has been having excellent results.
Now my concern is the removal of matter from the water that is actually good for the fishes!
Would this not provide an environment too neutral for the fish?
He had 8" sharks and an oscar, as well as a mean looking fella who was approx 1 foot long!!
Any thoughts on using these cannisters with maybe other filter media to provide filtration for aquariums?

[Lady Hobbs]

Sorry you didn't get an answer to your post and I probably shouldn't answer either as I don't have a great answer for you. I do feel if you are using totally softened water, that perhaps suppliments should be added to the water. It certainly won't hurt the fish any.