Well, it looks like gluten is not sufficiently developed. I'd suggest the following checklist. Answers on these would help us help you:
- Flour type / Brand (BF is way too generic ;-))
- Do you mix your dough by hand or mixer
- Are you using cold / warm temperature water to mix your dough
- Are your S+Fs every 3 minutes as you write or every 30 minutes as they should probably be?

- Dough temperature during bulk (while you do your S+Fs)
- Do you test your gluten strength (windowpane) before and after the S+Fs?
Friendly advice, if you're not familiar with high-hydration doughs, as mentioned by Rolls, start with 55% hydration first, get familiar with managing dough and shaping pizza, then take it from there. 70% dough should not be your training wheels dough, it will be a very steep learning curve.
If you're already familiar with high hydration, I'd first use only part of the water (around 55-60% hydration) to develop gluten, make sure you have a decent windowpane, then add the remaining water little by little all the way up to 70%. This, called bassinage by the French, is a technique that should work in your case.
If you're using a mixer, we can take it from here once you share with us the specifics.
Hope this helps.