Well for your 180 there are a couple i recommend. I tend to like in sump skimmers more than HOB's but here it goes.....
Octopus reef skimmers --- amazing
Corallife skimmers- they are okay but you can get the 220gallon rated one and it will to amazing
marineland skimmers-- get the 300gall skimmer for 200 off ebay, i personally use this one and threw away a trigger system for this one. Its very underated.
I would search ebay for any of these and use them on your 180
Octopus reef skimmers --- amazing
Corallife skimmers- they are okay but you can get the 220gallon rated one and it will to amazing
marineland skimmers-- get the 300gall skimmer for 200 off ebay, i personally use this one and threw away a trigger system for this one. Its very underated.
I would search ebay for any of these and use them on your 180