I have never used them so I used too much and the water in my 20 gallon Tetra tank turned very brown. The fish didn't seem to mind, but I had to tweak it a bit to get the right color and pH. These cones are very effective. After a week my tetras started doing more ballroom dancing so I think they like it. Since you only need a 20 gallon pair I would say this bag is a great deal.
12 Count Greenpro Root Tabs Fertilizer Tablets: Ideal For Aquariums, Ponds & Water Gardens!
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