Even a 75 gallon tank can easily cost thousands of dollars to set up and run. $30-40 on a bag of crushed coral is pocket change in this hobby, to be honest. I totally understand you are trying to save money and not waste the crushed coral you bought - all of us want to save money
but it's going to be MUCH more costly and time consuming in the long run if you use the crushed coral simply to save $30.
You might want to think twice before taking suggestions from your teacher regarding tank maintenance. You're going to have a hard time finding anyone in the hobby who says you won't have to do water changes. They should be done weekly and monthly at minimum. While monitoring pH is important, that is one factor in a lot of levels that need to be monitored. Altering pH isn't gong to change your ammonia, nitrates, nitrites, or other factors.
Fluorescent lights would be okay as long as you aren't going with corals. It doesn't have a high enough light output to provide corals with the lighting they need, and they would not survive in that environment. For a fish only though, it would be ample lighting. I started with fluorescent lighting too, but I upgraded to compact fluorescent in order to help bring out the colors in my fish.
Good luck! I hope you are able to find the answers you need.