Dan, my belt has 25 lbs of lead on it. That keeps me at what I call neutral, in other words I do not float up or down from the depth I dive to. I weigh 205 lbs and wear a farmer johns wet suit. If you weigh more , you will need more weight, if you weigh less than 205 lbs you will need less weigh. Just add or subtract weight until you get it right.
Also if your diving down 20 feet, I highly advise you to study a decompression table. Ron