Hey, is this the 45 that you picked up from me? 
Anyway, I agree that you should move the odd one out to a different tank. I don't think that your 20 will be overstocked if you move the ram in there.
I actually had a really similar situation a few years back. I was keeping 4 Bolivians in a 29 gallon, and although none of them ever decided to pair, there was one that got picked on quite a bit by the other 3. I ended up moving the 4th fish to a 20 gallon with some gold pristellas and a BN pleco, and it lived there peacefully for a couple more years.
For the record, this is why I advise against keeping more than one pair in a 29.
LOL

Anyway, I agree that you should move the odd one out to a different tank. I don't think that your 20 will be overstocked if you move the ram in there.
I actually had a really similar situation a few years back. I was keeping 4 Bolivians in a 29 gallon, and although none of them ever decided to pair, there was one that got picked on quite a bit by the other 3. I ended up moving the 4th fish to a 20 gallon with some gold pristellas and a BN pleco, and it lived there peacefully for a couple more years.
For the record, this is why I advise against keeping more than one pair in a 29.
