I don't think you need 6 bulbs - if you stagger 5 bulbs and keep the high light animals a little off the sand bed you should be fine.
I like the 60" bulbs - I use them on my 125 (with individual reflectors), the only problem is that I always have to order them because nobody local to me...
Your dosage will be dependent on the items in your tank and also the 2 part solution you plan to use.
If you have more SPS and clams you will need to dose more, if you are mostly softie and LPS you likely will dose less.
Also, make sure you have calcium, alkalinity, magnesium, and pH test kits...
I run 2 AquaClear 70s on a 45 gal. In one I have carbon and in the other I have rock rubble. I like having the carbon, and I change it out monthly with my water change.
My plan is to convert one to a small refugium in the future with chaeto.
Whenever I change mine I just put a few gallons of RO/DI in a bucket and drop the supply pump for my GFO reactor into it. I direct the output to another bucket until it runs clean, then I put it back in the sump the way I had it.
Sounds like it is not working correctly. I also have a dual unit from them and it is just a single click. Perhaps the relay is not working right.
I would contact them with the information and see what they say.
Yea it seems 40mm is right - I found a website that listed it as a 50mm and unfortunately trusted the wrong website. Will be ordering 40 mm fans now.
I may even mod the hood to take a couple extra of the quiet fans. It would cool it and keep the noise down. I will report back if it works or not.