The pump head is the difference in water surfaces, not from bottom to top. So, with a hang on the back that should be a "not applicable" head calculation. I guess that is a complicated way to say don't worry about head height. To my understanding you need to be moving about 750 gallons or more per hour.
My guess is it "worked" because you ran a filter.. that has changed. We don't like filters because of all the bad things they harbor... the hobby has learned much in 12 years. With new methods your tank will be healthier and easier to maintain.
It is different than 12 years ago, back then I was into fresh water because they hadn't made the advances of recent in reef tanks. Filters are no longer recommended. You will find us recommending you remove the filtration stages and turn it into a sump and/or refugium HOB. This is a simple mater. ... I "think". Can you send us pictures of the HOB? What brand is it? If it is one of which long term experienced forum members can still relate to they can advise on how to convert it to a sump or refugium.
Now days it is recommended that you run at least a minimum of 1 pound of LR for each gallon of tank water. Most of us run more than that. The microbes and other creatures in the Live Rock are the filtration system. In your case you can buy dry "live" rock that is seriously cheaper and let it get seeded from your existing Live Rock. You will have to order it on line as most fish shops don't like to sell it, they would rather seed it and sell it as LR. Many of us like to run some LR rubble in our sumps, as well. You will be hearing more on that subject, rest assured.
Plus, after your OOPS you may want to run some carbon in a sock for a while to be sure all that nasty stuff is pulled out of your tank. How are those corals looking and what are they? Pictures of them would be nice.
Please post some current water chemistry testing data.
Do you run a skimmer??? If not, that is how it is done now. A skimmer removes the protein from the water and "gives" it to you to dispose of. It acts the part of the surf foam at a real world reef which pushes the protein onto the beach to be broken down by terrestrial creatures, plants, and the sun.
Stand by for other forum reefers to offer additional advice.