Could 'stirring-up' my PFS caused problems??

[U_Hoo]

Hello. So I have a 55gal tank that's been fully cycled for 3 weeks. I've had 2 clown loaches and one RTS for about a week and a half. We had planned to start adding cichlids tomorrow. Things were going great. Yesterday I noticed the previously crystal clear water was slightly milky. I assumed bacterial bloom...new tank...not unexpected. Today I tested ammonia and nitrite and ammonia is still 0 but nitrite is .25? I did a 25% water change 5 days ago and noticed the tank was smelling like unpleasant wet sand (NOT a rotten egg smell, more mildewy) so I stirred the sand up a bit. Did I release toxins by doing that? The fish still seem to be acting like they always have. Do I let it sit another day or start a water change now? There's nothing dead in the tank (only had 3 things), what could have caused this? Hmm...just occurred to me that I added the crushed coral last week and at the same time recharged my purigen which was dark due to driftwood I'm assuming. I added the recharged purigen back to my canister on Saturday as well. Would some Malaysian Trumpet Snails help with the sand maintenance?

Here are the tank stats:

0 ammo/.25 'trite/ 25-40 'trates (nitrates are high from tap)
8.0 ph 17 GH 4 KH

55 gal
AC70, Aquatop CF400uv with pads, seachem matrix, crushed coral, purigen
aqueon 250w heater - running at 80
air stone
PFS substrate, local rocks, driftwood

ps. about a week+ ago I posted a thread about a white fuzzy growth coming from one of the rocks; that disappeared about 3 days ago without me doing anything.

 

[fort384]

Sounds as if the cycle just did not complete. The milky water is certainly an indication of a bacterial bloom. While stirring sand has anecdotally caused problems in WELL established tanks, I really don't think in a tank this new that it could have had any adverse affect.