I have added a big bit of driftwood which has leeched tannins but i am pretty sure that would only drop the ph. Its a ar980t which is 245l running 2 filters. I do use Flourish excel and comp when i remember. It has java fern, moss, a lily pad looking thing (not sure what its called), thin leaf java and one more type of plant but im not sure what it's called.
Yupp i have done a water change and i also dosed up the tank with more ich cure since it came back and a ph regulator by seachem