Hi, I'm having the same kind of problem although i'm not adding any chemicals.
i have a 20 litre tank with 3 mollies and an alge eater and a few fake plants. I'v tried doing serveral water changes and cleaned the filter but yet my water still looks yellow. i've even used one of those magnetic cleaner things to clear the glass. the only things that goes into my water once every 2 weeks is a tank cleaner that degrades
ammonia and
nitrite and help maximaise oxygen availability. all it contains is natural micro organisms and ive only used it 2 twice.
every post ive read is about other people using chemicals and that can change the water colour but i dont. any ideas?