Marine snow is fine, but I probably wouldn't mess with adding it. Focus on simply keeping good water quality. You should be getting enough nutrients into the water simply through your feeding routine.
I saw that you have a clam, what type of lighting do you have? Clams, ESPECIALLY tridacna clams require high lighting, preferably MH in my opinion. If you don't have this lighting, or at least a nice 4x54W t5 setup with the clam up high, you should consider taking him back to the LFS. Before jumping into tridacna clams, you might try the easier clams which are still beautiful, like squamosas and derasas.
With all of the money you have spent on your tank, and your livestock, you will be wasting all of that if you're using tap water, that's my honest opinion. The key to running a great tank of any kind is starting with good water. (like papa john's, better ingredients better pizza).
Tap water used to contain a disolved form of chlorine to control microbial growth, however that came out of the water easily after sitting for only a day or two. However water companies now use chloramines to control microbial growth (chlorine and ammonia mix). This will not just come out of the water, in order to remove it without chemical treatment you would need to heat the water for a prolonged period of time, not just let it sit. Chemical dechlorinaters also have the nasty habit of breaking the chlorine-ammonia bond, and leaving a bit of ammonia left over.
On top of that, there are many various types of phosphates added to tap water by the water company in order to coat the inside of their pipes so as to protect them, these break down into simple phosphates in your tank.
It is VERY worth your time to invest in an RO/DI system. Your tank and livestock will look better.
BTW you instant ocean salt is designed for use with RO/DI water, not tap water, so to me that matters as well. IO is also rather low in calcium, and high in alkalinity. If you plan on going the direction of clams, and perhaps later SPS and other more calcium demanding corals, then I would recommend doing the miracle mix. 50/50 instant ocean and oceanic. I was very pleased with the results when I made the switch. but if it ain't broken don't fix it..
i'm rambling now.