If you only have 30 spiders and all those roaches you are defiantely doing something wrong somewhere for your colonies to decline.
I'm not sure on the way that roaches are kept in SA but there are a few rules that I follow that have definately seen my roach colonies reproduce way beyond what I need and I have 289 spiders .
Rules that I follow
1) Temperature NEVER allowed to be below 90F (32
o)
2) Roaches containers ALWAYS blacked out so that they spend more time breeding than hiding from the light
3) I ALWAYS use egg flats and NEVER go for the natural setup
4) NEVER NEVER NEVER EVER USE FEMALES FOR FOOD. I would rather NOT feed my spiders than use a female roach
5) ALWAYS feed a high protein diet. I use powered dry cat crunchies. Roaches have soft mouth parts and cannot chew on hard dried foods with any efficiency. If the food is powdered, they can eat it very easily.
6) I ALWAYS use fresh fruit which is mainly oranges and apples and changed every other day. My roaches dont get 'scraps' they only get fresh food that i would eat myself.(except the cat crunchies)
7) Always keep the dry and moist foods separate as the dry food will go moldy very quickly is allowed to get damp or wet.