I'm using AN sensi base nutes m8.. always do with no problems.. or very few anyway.. my temps are regularly 28/29 and at times hit 30 with basically no air movement or ventilation.. Im no scientist but i think that's prime for a shitty res with pH that even ANs pH perfect can't keep in range.. thats my guess anyway.. comin off the res ASAP.. in fact coming out of the autopot tray now to start.
Its always something isnt it?
Do you have an air stone in the res? Would that help the situation?