You may have a chance of a cynobacteria bloom or an extended and more aggressive algae bloom with that many decaying FW snails. If you have any hint of hair algae in your tank, all this excessive organics can make it grow out of control as well. I always try and cycle a SW tank as naturally as possible and not going too nuts with the amount of organics in the system. As stated above one of my favorite methods is cured live rock. If you use uncured LR it will start you out deeper in the hole, so to speak, leading to the same above mentioned problems. A new SW system will go through many fluctuations in the first weeks/months until it gets more established biologically. One of the "cycles" of the tank will be algae cycles. First you will get brown and then slower growing green algae and then finally coralline (assuming light/water parameters are sufficient). These cycles can be brief and not too severe or extended and overwhelming, depending on the amount of organics in the tank. It usually doesn't take a high nutrient load to start bacterial activity. Keeping the load in lower levels at first will help keep you from feeding other problems and will concentrate your efforts at starting the nitrifying bacterial growth only. A lower nutruent load at first will also make for a less stressful and quicker nitrogen cycle, which is much prefered for your tank inhabitants.
G.