I say to redo the tank over again, but this time try to find some pure organic topsoil without any manure in it. Then you can compare the new results to that of the manure topsoil.
Or you can go with some MGO potting soil, but make sure to add in some laterite which ever way you decide to go.
With my 18 gallon I go with the topsoil I mentioned, and enrich it with 3 different kinds of laterite (first layer pure laterite, floramax planted substrate, and black flourite), then I use the mud mixture of the topsoil with laterite on top of dry ferts (iron chelate, dolomite Ca & Mg, and muriate of potash). Then I cap the topsoil mixture with 1" of PFS, but I have a 2" thickness of the topsoil mixture.
15g Fluval Flex - Will be a planted shrimp tank