Hi and welcome to AquariumAdvice!
Have you ever used copper meds in the tank? If so I have heard it stays in the silicone, etc. and can leach out later. Inverts such as coral, shrimp, etc. are very sensitive to copper. It is lethal even in very small amounts. You can see why this is not good.
Other than that, I would recommend using 1.25 lbs LR
per gallon or more along with a good protein skimmer and a few power heads for water movement(very important, especially for corals) and the appropriate lighting for the corals you plan to keep. As a general rule of thumb you want a minimum of 12-15 x's per hour tank turnover- meaning the total gph
of all the pumps together should be 12-15 x's that of the tank. Here is an article on berlin method of filtration you may find helpful-