I have a 90 gallon with 350 lbs live rock system has been running for 7 years now and main problem that i had was fire worms was eating and killing all my coral. but i have since caught and disposed of the worms and at this time I have a yellow tang and a clown which are about 6 years old. My latest problem is I must replace my main pump it is a submersible 750 gph.I have been with saltwater for about 32 years.My first system was 29 gal. with a under gravel system back then we used dolomite gravel and damsel fish to create the bio it took sometimes 6 to 8 weeks and corals were only in very very large systems and even then they were hard to keep most hobbist only kept fish.
