A smart lfs would not take them if you mentioned any sort of illness. Your best bet is to tackle this problem. Give rhe forum members a recap. List it like this.
55g tank
2 hob filters
Running for 1 year
5 mollies 2 guppys
Ammonia .0
Nitrites .0
Nitrates .20
Ph 7.2
First noticed this 5 days ago and since then ... I tried a massive water change on this day and...
Pretty much allow the people to see what you have setup and whats going on as well as what you have done to try and fix it.
More people will be willing to help if they dont have to read 5 pages of the forum to get a better understanding to advise you.