To solve the problem you need to boil your wood for three hours or so before putting it in your tank. That should get all the chemicals out of it.

Some plants that seem to be falling apart - Water sprite and Java ferns immediately come to mind - are actually budding several new plants from old leaves. So those less than attractive leaves are something we have to just tolerate. (Sometimes water changes and longer hours for the lights make a world of difference for those budding leaves.)

If you missed a couple of water changes, as most of us do once in a while, that could be catching up with you. A big change can stir things up and if the tank has been neglected for a while, water changes of over 50% can even threaten to reverse the nitrogen cycle!

If you were breeding tetras or some other rainforest fishes, one might ask if you had put peat in a filter. That will get you tea colored water in a hurry.

Another item which ambushes all of us, once in a while, is that deposit of mulm (bottom debris) which we miss. These tend to hide in tank corners, in depressions in the gravel, under box or sponge filters, behind rooted real or plastic plants, or behind/under flower pots.

More serious cases are where that stuff gathers under an undergravel filter plate. If it is missed over just a couple of weeks, that is not usually too serious. If it is missed over a matter of months to a year, that can be a biological time bomb, threatening to even wipe out a tank.

A little over a year ago, on this forum, we discovered that those sneaky mulm deposits could also be the source of green water blooms. While they can actually be a source of food, growing on them, for small fry, they are usually unwanted deposits of organic goodies which are best siphoned from a tank and dumped outside in one's garden or lawn.

These possibilities may not be the cause of your tank's discoloration though. You don't have a little brother or children or even a cat dropping stuff in the tank, do you? ;)

Good luck in solving your mystery. And in the meantime, keep up the partial 20-40% water changes. :)