I really can't decide whether to drain or shock. Intex round 18' x 48" pool. Pool in kept up year round and winterized like a regular above ground pool. Last year water was as clean as could be at opening. This year when I pulled the cover off it was already green. It is about half full and I can see the bottom.
Advantages to draining: Quicker, less work, fairly low water rates and no water restrictions.
Advantages to shocking: Water already has salt and cya in it from last year, it may be cheaper than paying for water, extra salt and extra cya, I hate to waste water.
What should I do?