This is a place to share lessons I've learned.  It's where I remind myself not to overlook the obvious. Thoughts on algae Sometimes a tank that has been stable starts to decline, the water just isn't as crisp looking or small amounts of algae begin to appear.   It may be a sign that it's time to clean your cannister filter.  At least check the intake strainer to make sure it isn't clogged.  There are different thoughts on how often to clean.  When I start to notice a detritus buildup, it's probably time to clean the filter.  As the filter clogs, circulation is reduced. Another thing I've found causes reduced water quality is poor circulation.   It may be a clogged filter.  But a common cause I often forget is the plants themselves.  As they grow and increase in density, they will block water flow.  If your tank is really packed, try thinning the plants a little.  It may be all that's needed.  I was able to eliminate chronic algae in a tank by simply changing the locations of the intake and outtake for the filter.