I like blackwater tanks aswell. I have a 20 gallon orinoco river themed tank that has a black water look even considering actually putting leaves in it to tea it.In my experience, mulberry leaves don't stain the water much if at all. Not sure about guava leaves since I've not personally used them. Magnolia leaves will give you the blackwater look. And pre-boiling/soaking for a few days will definitely help get out some of the tannins and make sure the leaves sink. I personally really like the blackwater look, but if not, you could always use some charcoal or Purigen in the filter.
But the tank im doing to the dojo is going to be my living rooms center tank. i want it to be light and vibrant so my non aquarium hobbiest guest can not be confused why my tank is so brown and "dirty". lmao
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