Im switching my two part chemicals over from ESV to BRS. This was one of my concerns with cost associated with two part like I stated in the thread peredhil linked....http://www.3reef.com/forums/water-chemistry/2-part-dosing-vs-reactors-74496.html But after this thread I started I realized that Ca reactors arent necessary to keeping up with high demands. I now have my two part dialed in and prolly wont adjust it again for a few months to keep up with the growth. I see more potential problems with a Ca Rx.Not to mention the costly investment. Yea I like to drop $$$ on my tank... but if its unnecessary than no need. Id just be a fool. Jason Mckenzie here on 3reef uses 2 part on his 370 sps tank and has no plans on going back to a reactor. There are many others with large systems that use two part on their heavly dominated stony tanks. Food for thought.