If you are @ 18% BF you don't float. A typical 3mm suit will be about 3-5 lbs positive. Even with a buoyant al 80 (~4 lbs positive empty) you should only need about 8 lbs.of total ballast. Your reg provides about 2 lbs and a SS plate and harness provides another ~6 lbs.
22 + 2 (for your reg) is likely way more than you need.
Tobin
When I'm in Bonaire I'll be doing my advanced OW so I'll have plenty of time to test the perfect ballast.