What are these brown clusters on the substrate?

Can anyone please tell me what these brown clusters on the substrate are? Against everyone's strong recommendation, I caved to my sons desire to get fish in his aquarium and decided to use Tetra Safestart for a fish in cycle. There are 6 neon tetras in the tank and appear healthy. The brown clusters appeared out of nowhere in a very short period of time (less than a couple hours). I am getting the following test results:

PH: 7.2
Ammonia: 0
Nitrite: ~0 ppm
Nitrate: ~5 ppm

I dont want to vacuum it up because TSS advises against a water change. But, I do have 5 gallons of water set aside that I already treated with Prime in case I do need to add water before the tan is cycled. Should I vacuum it up, add my conditioned water, and add more TSS?

probably blue green algae (Cyanobacter bacteria). just suck it out with a gravel cleaner.

Yes I agree with Colin_T, vacuum it out. Changing water does not effect the growth of beneficial bacteria because very little of it is in the water column. So do water changes, start off slow because if your fish are now used to the condition of the water that is in your tank that has not been changed every week as it should be, to much fresh water at once can effect them. So start of with little water changes every week and increase it each time in small increments.

Just because you are not measuring much in the way of nitrates, and the other measurable units in your tank doesn't mean the old water is good, over time the chemistry of the water in your aquarium does change and gets further away form the chemistry of your water source. So if you wait to long to do a water change then it will and can shock your fish. The longer you wait to do water changes, the worse it gets.