Hello everyone, first post here so I’ve had a 55 gallon tank for over a year now with little to no issues, I recently bought a 75gal tank from another reefer who was getting rid of it. At this moment it’s cycling but I had a few questions. I saved a couple of gallons of the old 75gal tank and dumped the rest when moving it. I safety moved a few of the fish he had in there to my 55g tank and I kept the rocks in water until I had refilled the 75gal tank with new water. I noticed his tank was quite a few bristle worms and tiny brittle starfish which died during the process of moving. I rinsed it with RO water and placed it in the tank as well as the old sand and equipment. (I wanted to keep as much beneficial bacteria as I could). After a week or so with API water testing there was a HUGE ammonia spike with zero nitrates and now the ammonia is back to zero with nitrates through the roof and what I think is brown algae growing on the sand and rock. I know now i have to make water changes to bring down the nitrates to a safe level before putting in the fish. I guess what question are: is there any toxins in the water I cant detect from the dead bristle worms or starfish? Is the water safe, besides the high nitrate problem? How do I get rid of the algae? The tank came with AI lights, should I turn on the UV settings to kill the algae? Will this also kill the beneficial bacteria? Or should I completely turn them off since the algae is only growing where the lights shine?