The amino acid chelate forms of selenium have low toxicity levels, I dont recommend more than 100 mcg a day of those. I actually dont recommend them at all. The plant and yeast based forms are MUCH more tolerable at higher doses. People treating viral infections like hhv and AIDS without drugs seem to consider 800mcg a standard dose and Ive read reports of candida infections clearing up at 800 mcg, it was even written about in the Immune Restoration Handbook. Ive read of some using up to 1600-2000 mcg, though not everyone can tolerate doses that high. Side effects like headache and muscle pain/spasm pop up and will usually resolve within 2 or 3 days of stopping supplementation, I have yet to read of any cases that were any worse than that. I recommend phytosel. You could try 400-600 mg a day.