Choosing a skimmer - concerned about tuning

Hello,
I have a 180gal FO tank that is running without a skimmer, currently
relying on a wet/dry and live rock. I want to add a skimmer to get the
water quality up and to help battle phosphates and algea. My stand is only
26 1/4" from the floor to the bottom of the tank. I have plumbed an
extension on my wet-dry by drilling an old 10g tank and using bulkheads. My
plan is to put a skimmer in the 10g along with the return pump, then remove
the bio-balls from the wet-dry and use it for maco algea.
I have looked at the ETSS Evo 500, AquaC EV-180 and Euro-Reef CS6-1.
What is not clear and is a concern to me is how these units might need to be
setup and/or adjusted to work properly. With the limited clearance under my
stand, the unit will have to sit on the bottom of the 10g tank and any
adjusting will have to be done via a gate valve.
Any comments/recommendations are welcome - the Grinch I work for gave me
a bonus this year and I hope to purchase something before Christmas.
Happy Holidays to all
Henry