What should I add?

[barryla61]

I've been growing tomatoes in tubs for years now using my own mix of composted manure, potting mix, compost and some sand. I know this is not "the reccomended tub mix" but it works well for me, at least I think it does, the plants always grow out of their concrete wire cages - 6 ft.
Just cleaned and bleached my tubs and I'm looking for any suggestions as to what I might add to make my mix better. Peat? Pine bark fines? Perlite?
Thanks,
Barry