I don't think anybody has tested the theory so it's hard to say. A lot depends on what you mean by over dosing and also what tank setup you have. TPN+ does contain ammonium so this will cause problems if allowed to build up. Dosing high levels of TPN+ on a new setup can and has for some people caused problems with livestock. But do the same on a mature CO2 enriched densely planted tank and it shouldn't be an issue.