Install Hydrostatic Valve or not?

[Vince-1961]

I put my scuba gear on this morning, swam to the deep end, removed the main drain cover and discovered that the pool in my new house does not have a hydrostatic valve. Instead it has what appears to be a standard threaded PVC plug with the 1.5"-2" square top screwed into a hole where I had hoped to find a hydrostatic valve. There's a drainage canal at the back of my property, the water level in which is probably around 7-8 feet lower than the ground level of my yard. The previous owner told me that the water table is 7-8 feet down. The pool is 7.5" deep. I want to drain and refill, but am understandably cautious about floating (popping) the pool. So I watched a video on YouTube (the link was here on troublefreepool) of a diver replacing a hydrostatic valve while the pool was full. It looked fairly straightforward and easy, but I am concerned about how much water might drain into the ground during the process. Could it be enough to float the pool?

Any thoughts, comments, instructions or opinions would be most appreciated.

 

[mas985]

Hydrostatic valves are insurance against the pool floating but they are not 100% either. Over time, the valve can stick so they do become unreliable.

In your situation, I would suggest a no drain refill.

Refill Experiment

Every year I need to replace at least half of the pool water due to high calcium but this year, instead of a traditional drain and refill, I tried something different. I had read of people doing an in place refill using plastic to separate the new water from the old water. So I thought to...

www.troublefreepool.com

Draining - Further Reading

www.troublefreepool.com

 

[SecoSteve]

Can you share why you want to drain and refill?

There is also a thread here somewhere that showed a no drain refill where they put new water on top of a large tarp on the pool, and drained the old water at the same time to avoid mixing the two types of water. It was pretty cool to watch.

 

[ajw22]

There is also a thread here somewhere that showed a no drain refill where they put new water on top of a large tarp on the pool, and drained the old water at the same time to avoid mixing the two types of water. It was pretty cool to watch.

The tarp method of draining a pool may look cool but it can be dangerous to people or animals around the pool and we don’t recommend it.

 

[mas985]

+1 ^^

Not only that but the tarp isn't need as long as you take water temperature/density differences into account. In the experiment I posted above and repeated again recently, I got close to 90% replacement without any dilution.

 

[Vince-1961]

Off the chart CYA (100+)

 

[Vince-1961]

I just happen to own a tarp large enough to cover the whole pool. (It's been in an attic for 17 years, so hopefully it won't disintegrate when I unfold it.) I like the tarp idea. No animals or humans (other than two responsible adults) to be endangered, so yeah. I like that idea.. It's a tri-chlor pool, so I can't reliably drain from deep and refill from shallow. Converting to salt when the parts arrive, maybe next week.

 

[Vince-1961]

It turns out my tarp was about a foot too short and had a few holes in it, but it did admirably well is separating new from old water. So, it qualifies as a partial drain and refill. New numbers:
CYA 40
pH 8.0+
FC 1
TA 7
CH 0

Looks like I'm off to the store to buy some stuff......