DIY backgrounds?

[Jaster]

I been looking at some these DIY backgrounds, caves,... but I hear they cause Ph and such to shoot through the roof and really can mess with your tanks numbers. I really dont want to spens so much on rocks to make my new tank look nice. Some of these projects look great.

So my questions are:
1. how true is this?
2. is that just cause by not curing and or soaking them long enough?
3. what are people thoughts and maybe some suggestions on doing these projects?

Thanks all!