Oppinions? 200L/55gal tank?

Your tank is fully stocked. Anymore fish & you'll create problems for yourself & end up having to clean & water change twice a week, & start losing fish to ammonia/nitrate problems. Tannins are created by wood that hasn't been soaked long enough & have started leaching colours & tannins into your water. Remove whatever wood you have in there, place in a bucket & soak for at least a week. That should remove the tannins. And in the meantime do a 20/25% water change (as usual) & replace the water, then again before the wood goes back in, this should clear things up.