Small/Young SAEs are good grazers IME, but the adults are worthless- all they want is fish food. I traded them off but had no problems before that. They were in with rainbows, so not much likelihood of their bugging those speed demons anyway. The few I have kept since were traded by the time they doubled from purchase size.
My best suggestion would be to get the CO2 concentration up a good bit. At 4WPG, you need to be nearly a full pH log down at least. If the tank at is at pH 7.0 de-gassed, you should be at or near pH 6.0.
kcooley - IME, "starving" the tank/plants is an invitation to algae, and phosphate is a macronutrient for plants - its absence or very low titer is an invitation to algae.
Edit: Thanks for presenting so much info - life would be sooo much easier if that were routine on the boards.