Fighting Algae with Borax

[Sumo1]

Our church pool is drained each year and when it's empty, groundwater comes up through the hydrostatic until it finds its own level. When the pool is full, the weight of the water and the water pressure is enough to keep it closed. The hydrostatic valve is located beneath the drain grate in the deep end of your pool. You have to remove the grate to see it. The valve on the church pool is a 1 1/2" pipe with a cap that is attached with a hinge on one side. There is an O ring below the cap and it is spring-loaded so that the cap is closed when something is holding it down (ie. water/pressure). During the winter, we put a large rock on the valve to slow down the influx of water. As I understand it, almost all pools built in the last 30 years have them, and they are probably required by local building codes in most areas.
Hal

[topless]

I know exactly where the valve is now, I wondered what that fitting was under the main drain grate.
I realized I have another path for dirt into the pool. When this pool was installed, it has no concrete on the west side. On the other side of the brick lip are landscape timbers and they are cut into a berm that rises 5-6 feet above the pool in about 15 feet. I vacuumed the pool today and that side had a lot of dirt on the bottom. Even with the cover closed, a hard rain could wash dirt down the hill and into the pool. One of my projects was to dig out that side and put a retaining wall 3-4 feet back so we could walk around the pool. Now, I have another reason to get that done.

[Tredge]

I dont have a valve like this. I have a very old concrete pool and the bottom intake is all sealed up now. The pluming under the pool has been broken long since before I owned the pool.

Doesnt really matter as I am on top of a gravel area with a low water table.

[jenpen400]

Thanks for the info on the borates finally zapped the alge and the pool is soooooooooooooo clear.

jen

[topless]

Here's an update for 2008. I closed my pool last year late, waiting for the temperature to get down below 55 degrees. I did exactly what was recommended, including adding polyquat for the first time. We had an extremely long wet winter & spring. I finally opened my pool in late May and the water was clear enough to see the main drain. However, all chlorine was gone and the water was just starting to cloud. I added 1.5 lbs of CYA, 3 bottles of bleach and started the pump. I tested for borates, it was still 50 ppm.
We didn't swim until the last week of June (I'm a sissy when it comes to water below 78 degrees), but I have had zero algae, and used about 1 bottle of bleach per week to keep the water crystal clear. Only needed more when cottonwood trees were covering everything, this year was really bad because of the excessive amount of rain. We passed the yearly rainfall average by the middle of June.
Do borates inhibit algae growth? Yes.

[topless]

I regret to say, I found mustard algae in my pool today. Not real bad, but It's back to 24ppm shock for a few days.

[chem geek]

Sorry to hear your algae came back.

Borates (boric acid) are a mild algaecide, not a strong one like sufficiently high levels of chlorine or copper (but that can cause staining). It's possibly a little weaker than PolyQuat though that is just a guess. Mustard/yellow algae takes about twice as much chlorine to kill it as regular green algae and it probably takes a stronger algaecide to inhibit it.

A chlorine level that is 15% of the CYA level seems to be roughly the level that inhibits its growth and is roughly the "Max" column in Ben's Best Guess CYA Chart. Killing an existing outbreak can take an FC level that is 60% of the CYA level over several days and making sure that you get behind light niches, soak all poles, etc.

Richard