First off DA has the worst customer service ever... I just added a new Pk4 to my Reefkeeper LITE to make it two. It was working fine until I updated everything and programmed my settings. Then it went cahoots and the RKL won't see both but if I shut either of them off I could see the settings of which is left on... It's not the Bus cords because I have an extra one and trial and errored it out... I don't know if it's the RKL or maybe the PK4 or hopefully someone has a suggestions because DA really stinks with their help...thanks