This is the toilet tank in my apartment. A few days ago I started noticing brown residue in the water. Upon investigation, I encountered a toilet tank I'm not familiar with... there's an "outer" tank, which is the one that fills with water, and a smaller, inner tank, which gets its water supply from the outer tank and is where, from what I can gather, the toilet actually flushes.
However, as you see from the pictures, while the inner tank is clean, because it always empties upon flushing, the outer tank only empties about halfway through, and the algae keeps accumulating and never reaching the bottom.
I've poured some bleach and started using those pills, but I'm not really familiar with this kind of toilet. Is it normal for the outer tank to not flush all the way down? It seems like a very strange and counterproductive design to me... the little white tank has "patent pending" written on it.
update: Looks like this is the toilet model http://youtu.be/2SzVAwPAuJ0