to drain or not to drain...

I'm buying a house with a 35K gallon IG gunite pool. The pool is probably 30-40 years old. The old owner was 90 years old, and I don't think she used the pool at all in the past few years, but probably had a service come by regularly. Every time we've gone to the house there has been a floating chlorine pack in the pool.

I think they cut back (but didn't cancel) the pool service when they put the house on the market, which was 6 months ago. It now has black and red(?) algae growing in it. I was told by the pool inspector (and have read on the forum) that the only way to really get rid of black algae is to empty it and scrub the affected spots; otherwise you just control it so it isn't visible. The pool inspector wants to service the pool after we buy, but he was already talking about all the chemicals he would use on it, and I want going to take a crack at it myself, anyway.

It's in SoCal (earthquake country) and has a crack on the bottom of the pool. It's long, thin, and straight, basically centered down the ramp from the shallow to the deep end. The skimmer also has a crack in it. The inspector did a leak test and said the pool is not losing water through any cracks.

About 5-10 years ago, the pool was acid-washed, and he said the plaster is not in great shape (because of it?). It does look stained and kind of tired. With all of the other upgrades we need to do, we won't be re-plastering the pool for another year or two.

So my questions: Should I drain the pool and refill it? I've been told that you need to replace the water from time to time, but I thought I read here that you don't. (It seems that you are replacing the water if you're adding 1/4" per day to replace evaporation.)

I don't get the keys until the end of this month, so I can't test yet, but I believe the floating chlorine packs include stabilizer, correct? If so, might decades of chlor-pak use raised the stabilizer to astronomic levels?

The inspector said he could grind out and fill the crack with plaster, but that in the next small earthquake it would probably just crack again. I would kinda like to caulk it with a white silicone caulk (bad idea?) just to hide the crack, even if it isn't leaking.

To Drain:
1. "old" water that hasn't been changed in 5-10 years (possibly very high stabilizer levels)
2. caulk crack on bottom
3. scrub black algae spots directly (possibly bleach out some other stains as well)

Not To Drain:
1. Unnecessary(?)
2. Minor waste of time if not needed
3. Moderate waste of money (cost of 35K gallons of water)

Thanks in advance

Water doesn't get "old" and rarely needs changing.

A much bigger problem of draining is ground water--it can turn your pool into a boat, even though it's concrete, and float it right out of the ground. Very, VERY expensive mess! If you don't have ground water, it's not a problem.

MUCH better than caulk is underwater epoxy, available at any pool store. Usually it's grey, and sets up nicely underwater. But it sounds like the pool needs resurfacing.

Others can offer more substantive advice.

Carl

moving this . . .