The rusty looking allege might be diatoms, which happen during the cycle. Your tank is only 4 weeks old and unless I missed something it appears it's was populated as part of the cycle, not after. The fact that you still have nitrites is not great IMO
. What is the Nitrate level ?? Also what size is your tank?
Last thing, for clams you are going to need some serious lighting. What do you currently have?
55 Gal FOWLR
105 lbs Live rock from LR
2 Yellow Tail Damsels
2 Green Chromis
1 Emerald Crab
3 Peppermint Shrimp
4 Scarlet Hermit Crabs
1 Blue Knuckle Hermit Crab
1 Large Turbo Snail
Hitchhickers: 3 Purple sea urchins, lots of rock crabs, pistol shrimp, brittle stars, snails, worms, etc.
and aiptasia, aiptasia, aiptasia (it was free $$)