I am new to fish tanks in general, I started my reef tank around July and had multiple fish in it, including clowns, a tang, some Chromis, a wrasse, and other starter fish. Unfortunately, I got ick which whipped out all of my fish. I decided to completely clean the tank, change all the rock, replace all the filter media, etc. After letting the tank sit for a few months I decided to start again fresh, I bought fritz turbo start 900, cycled my tank perfectly in about a week. I saw the ammonia levels increase, then decrease, the same for the nitrite levels, and eventually, the nitrate levels increased. I did a 25% water change to lower the nitrate levels and planned on getting two clownfish the next day since all of my water parameters checked out. The same day I scrubbed off what appeared to be a build-up on the side of the tank, it was a kind of tannish color, I am not entirely sure what it was (maybe algae or sand), and the next day I tested my ammonia, nitrite, and nitrate levels, and my ammonia levels shot up to the highest possible level for my test kit. I gave my tank a couple of days and my ammonia was still extremely high, but my nitrite and nitrate levels were fine. I am not sure what to do at this point, but any guidance would be appreciated.