Rusty Looking Deposit

I wasn't sure where I should put this but I fear it may affect fish or plant health so here it is.

I have spotted a rusty deposit on my spray bar. Could it be from the water supply or could it be a chemical reaction in the tank? The plants I have haven't really shown any signs of growing over the last week or so. Any ideas what this is and how to take care of it?

I'd agree with Skittler.
It looks very similar to the stuff around my heater.
It brushes off very easily.

Brown deposits are usually diatoms which are indeed common in new tanks - they like ammonia, and you had a fair bit of that in your tank during cycling.

It might get a little worse, your plants might end up with a dusting too. It usually disappears of its own accord after a couple of months.