What algae do you have now? have you reduced the light period?
I killed my loaches with excel too. It greatly reduce O2 in a tank. Try H2O2 at 1.5 ml/gallon. Spot treat or the whole tank with the filter off for an hour. Spot treat is better especially out of tank.
Try cutting NO3 & PO4 completely. Just dose K and micros. Fish waste should be enough for N & P.