First, I meant FTC, not FCC
But I'm sure the FCC has something similar
Second, it's not about signing any FTC thing, the idea is that you have to be forthcoming with the fact that the company is sponsoring it, or sent you a "sample", or whatever so that there's no conflict of interests about the true intentions of what's going on. Which is that it effectively is an advertisement for said company, and any prospective customers of said product know that what you say about the product MAY be influenced by the fact that you received some form of compensation for it whether monetary or physical goods.
Suppose you meet someone who tells you about a great new product. The person says it performs wonderfully and offers fantastic new features that nobody else has. Would that recommendation factor into your decision to buy the product? Probably.
www.ftc.gov
Chances of "getting busted" by the FTC are really slim, however simply stating in the first post whether it's Instagram, Twitter or Youtube (and possibly forum posts, that part I'm fuzzy about) about any items that you received gratis or compensation from companies when doing any sort of review or build pretty much covers all your basis. So if Kessil sent you a light, or sold it to you at a deep discount, or the "diffuser", or if the tank was in any way gifted, or the pumps, etc etc etc, simply mention it and you're in the clear.