Hello All, We recently lost almost all our fish to marine velvet after upgrading our 90 gallon system to a 125. Many mistakes were made - we had our LFS design and install the new system hoping to avoid headaches. Massive mistake. Bottom line - in 5 years our 90 gallon system never had a severe disease outbreak. We had a few fish that got sick but they recovered with vitamin supplements. We had a UV Sterilizer on that system. Within 2 weeks of the new system fish started dropping like flies. We are fishless in our display for now, 4 survivers in an emergency QT. Planning to let the display sit fishless for 76 days to be completely sure the parasites are gone. But we never want to go through this again. Our new system was installed with pvc plumbing. We have a sump with 3 chambers - filter sock, fuge and the final one where our skimmer and return pump are located. The guy who installed the system is recommending a drop in Uv Sterilizer - claiming we have more control over its flow rate. But I've seen online these systems don't work. They don't move enough water and they recirculate treated water making them inefficient. Though we've been doing this for 5 years we are not that schooled in all the tech. But I no longer trust this guy - I don't think he meant to cause us trouble (he insisted after a week it was safe to add 9 new fish - I was surprised but he said it would be ok - it totally wasn't) but his bias is to sell. Any recommendations? My plan would be to figure out how to do this myself.