Internal Parasites? Help please.

[Colin_T]

If you post a picture of the filter we will be able to offer more advice.

salt is fine with medications.

 

[Care_bear]

Sorry I thought my previous picture of the pump label would be what you needed. Here is another picture, but this time of the whole pump.

Another (smaller) fish is now loosing weight, and sinking down to the bottom frequently and hiding in the gravel.

The salt is on its way to us.

 

[Essjay]

For a small tank like this I like sponge filters powered by an air pump. This is the one I have in my 23 litre betta's tank https://www.aqua-one-spare-parts.co.uk/proddetail/aqua-one-air-driven-filter-30- Mine is powered by an Eheim air pump.

But bear in mind that you can't take the old filter out and replace it with another one. If you were to get the same sponge filter as me, it has a hollow core so you could put the sponge or whatever from the old filter into that core.
The current filter has a lot of beneficial bacteria living in the media. Without them, ammonia and then nitrite will build up and harm the fish so you need to somehow keep the old media. The usual advice to run both filters together for a few weeks won't work in this tank as that would create even more water flow.

 

[Care_bear]

So the current pump/filter(all in one) has a Qmax of 320 l per hour. We need a pump/filter with a lower L/h.