Matt,
I ditched my VHO retro kit after about 4 months when i first set up my 180 - I had space issues - VHO's are bulky IMO, but nice color.
Are you using them for lighting or color purposes? 320w of VHO is crazy, again, IMO.
keep in mind that IceCap Ballasts will overdrive the T5 as well.
Sounds like you're down to the nitty gritty - so close you cna smell the salt
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House
When you got rid of the VHO, what did you have running on your 180?
Nothing. No supplemental lighting at all. He ran four Phoenix 250w DE on BlueWave 3 ballasts with Reef Optix reflectors. The colors were still amazing......landed his 180 the notoriety of being Advanced Aquarist TOTM in November, 2006.
swimmer
Perhaps I should keep my opinions to my self considering the top reefers talking here. But what the heck. In my tank I run two 6' VHO actinics, 1 superblue & 1 white actinic because I don't like that dark tank look. By combine the two my tank as a nice mello look to it. I run my VHO's 12 hours a day, and my MH three XM 175 watt 10K for 6 hours. The MH run for less time due to electric that they pull. And my animals seem to be happy with this combination which is what is most important to me.
making the animal happy, is the first priority... this begs the question of what type of animals are you keeping. This tank will be almost entirely SPS.
By the way, the way my bulbs are set up is 1 VHO in front, and the other is behind the MH(3 MH bulbs) my tank is 6'.
Hey Matt... The entire system is going to be in your basement right? The Dart will not be able to effectively pump water up to a second floor if you are planning on having the sump room in the basement and the display upstairs. I have my Dart spilt two ways right now and I'm sure it has lost some GPH from head pressure, change in pipe diameter, etc. Just something to keep in mind. From your diagram it looks like the bulk of your water is going into 2 returns and the chiller which I think you should be fine with.
Cool. Thats a good idea on having a backup. I really should do the same. BTW I have VHOs as well and I think I have it on slight overkill by having 4.