diatoms nitrates silicates

OK, this is going to be long...   Tank started Oct 2011. ~150 l, SG ~1.002 @ 25 C, pH ~8.2, NH3&4 0 mg/l, NH2 0 mg/l, NH3 50-100 mg/l (tap 40), sand bottom. Population as per below. July 2012: added 10 Vallisneria and 6 Boesemani Rainbowfishes. November 2012-now: bloom of diatoms. I always...