I am pretty new to this but if your tank doesn't seem to want to cycle in a decent amount of time then most of your beneficial bacteria probably died a long time ago. I used Microbacter7 to help seed my tank along with live rock and live sand. The Microbacter7 worked great for me and really helped move the process along.
After confirming the cycle with fish-less cycling it can convert 3ppm ammonia to nitrites then to nitrates in 24 hours. That entire process was done over roughly 5-6 weeks. If anything I have too much beneficial bacteria at this point and it will reduce to the current bio load of the current livestock, which is fine.
It appears I never actually had enough ammonia in the beginning to even start a large initial cycle. Lesson learned: verify you have an ammonia source and can get a good reading, else you will be surprised down the load like me. Especially since my tank was brand new and had no established filter from another tank. It should naturally have a noticeable cycle in this case.