Gunite pool heavily pitted over winter

Just bought a house barely a year ago. The pool had been re-plastered maybe 8 years ago. It was in ok shape.

When it got too cold to swim I covered it and let it go. It turned into a swamp. I shocked it with bleach and cleaned the filter and it's crystal clear blue now and 75. I jumped in today and the plaster is incredibly rough and heavily pitted.

So my question is--what did I do wrong, and what should I do to fix it? Is there a DIY fix for the surface, or am I stuck hiring a contractor? I'm very handy--and I can't afford to drop $5k-$10k having it replastered!

Specs: Pool is In Ground, approx 28k gallons, SWG, in Socal.

What's your pH and Calcium levels?

They are good now, the PH was probably high during the 4 months or so though. I've got some DE leaking into the pool because I have 4 filter elements that have damaged connectors... It doesn't feel like it's DE that's causing the problem though. Would the PH being high for a few months do that?

If your calcium level (Calcium Hardness measurement) dropped too low, calcium will be removed from the plaster surface probably causing your problem.
Al

Or if your PH, Alk, calcium got too high, your might have scaling. Sometimes that can seem like pitting.

To fix it, there are a few choices that I know about:

1) Replace plaster. $$$$
2) Drain and acid wash. Unless you are daring, it requres a professional.
3) Lower PH and alkalinity and brush brush brush. This much like an acid start of a new pool. The idea is similar to 2 but does not require a drain but does require a lot of acid and baking soda. You drop the alkalinity to zero for a few days and brush the pool three to four times a day. Then you add the baking soda to rebalance the pool. Note that this method like #2 will reduce the surface life somewhat but it is much less expensive than #1 or even #2.