CYA off the "best guess" chart. Advice?

[geoeremite]

We just bought a house that has a IG plaster pool that I'm guessing is about 22kgal (somewhat irregular shape) and have been trying to get it in order while preparing to move in. A good friend pointed me at this site and I'm immensely thankful for it.

My CYA seems to be off the chart... probably above 250ppm. I've read all the recent threads on high CYA and understand that the choices are pretty much dilute or run higher Cl. The water table is really high and we just had our wettest March on record, so I'm leery about the drain-and-refill turning into a drain-and-float. I'm thinking I'll drain 25% or so, refill, then repeat over the course of a few weeks to at least get it partway down. Or I could just extrapolate the "best guess" chart. Thoughts?

Here's some more background:

Yes, the previous owner loved their pucks. Yes, the pucks are gone.

I'm guessing the pool was last drained when resurfaced about 7 years ago. Not really any winterization here in rainy California.

The water has been clear (i.e., I can see the drain clearly) for at least the last three months (when we first looked at the house), although there was plenty of pine needles, dirt, other debris, and a family of earthworms in the pool when we took possession at the start of the week. I'm pretty sure there's been little-to-no maintenance done over the winter.

I've had the pump and Polaris 380 running a few hours each day to sweep up. The cartridge filter was running about 35psi, which I've now cleaned (lots of earthworms parts, *really* nasty slime, and other grossness). Backpressure dropped to 16psi. The Polaris started flicking it's tail in joy after that cleaning .

I also discovered that the skimmer float valve was broken and, in the process of replacing it, found a good sized wad of pine needles and *stuff* in one of the two pipe openings below the skimmer. The wad is gone and I have the replacement valve to install tonight.

I've pre-ordered Ben's test kit. In the meantime, I used the former owner's DPD kit to check Cl and Ph, getting 0 and about 8.0, respectively. Added 1 gal 10% Cl and 16 oz ph down (also left over) yesterday morning.

I then found the CYA and FAS-DPD test kits at Leslie's, so this morning I used them to check the effect of yesterday's work. My Ph was down to 7.8 (expected lower), and the FC was at about 4.6 (expected much lower or 0) with CC of 0. I was surprised by the FC and that's when I started to suspect I wouldn't like the CYA measurement (see how well the forum educates? ). The dot "just disappeared" with maybe 1/4" in the vial and so far away from any marks that it wasn't worth guesstimating .

Wanting a second opinion (first pool and all), I filled the Leslie's water sample bottle and (skeptically) let them take a shot. Here's their numbers:

FC 4.8
TC 4.8
Ph 7.9
TA 170
Ca 375
CYA 275+
TDA 1000

They also used the Taylor CYA kit but couldn't get a meaningful reading, so the other, more experienced guy, used a test strip (yes, I know) that went up to 300ppm and with those the CYA was just a shade below the 300ppm max color. I have to say they did a good job by recommending that I not buy anything since I should consider at least a partial drain-and-refill.

Anyway, sorry for the long post. I've been accused of being somewhat AR about things and know the lack of background can make helping harder.

thanks,
--Scott (a happy new pool owner )

[KurtV]

It reads to me like you have a great handle on things. Your 25% drain and refill routine should work fine but you probably don't want to wait weeks in between sessions. I'd drain, refill, test, and immediately repeat until your CYA level is where you want it. In the meantime you probably want to get and keep your FC very high (maybe 15 ppm?) until your CYA is back on the chart.

[duraleigh]

Hi, Scott,

I'm with Kurt....you've got a great handle on understanding your pool chemistry...wish I had learned that fast.

If you do 25% refills, it will take 7 of them to get your CYA below 50. If you can tolerate a 50% refill, you can do it in three.

I also assume that TDA is TDS (total dissolved solids) and that's a little high as well. Drain and refill will sove both issues.

You're off to a great start...enjoy your pool!

Dave S.

[mwsmith2]

Also, if you want some overkill in figuring out the dilution of your pool, you can grab my calc in my sig. There's a dilution section in there that you can put in the size of your pool and it will tell you a percentage drain to get to a number that you want. Either that or you can fiddle with the numbers to see where you would end up from a partial drain. Either way, it's something to play with.

Oh and there's another nifty way to do a water change without floating your pool. What you need is to source a HUGE sheet of plastic. Throw it over your pool. pump water out from under it with the pool pump, and refill on top of the plastic. As you pump out from under and refill from the top, the plastic will sink down into the pool. The plastic will keep the water separate, and you can actually change 100% of the water in one shot this way, if you can find a sheet of plastic big enough. This is a trick that vinyl pool owners use to change water without ruining the water.

Michael

[geoeremite]

Thanks for the great feedback, that helps a lot. Yes, I meant that TDS was 1000.

I'll probably do the 25% at a time solution, although the plastic trick is a really neat idea. I figured out last night that the water doesn't cost any where near as much as I feared, which is also reassuring.

Michael, I've seen bleachcalc and wanted to give it a try (sounds great), but I guess that's one of the (few) drawbacks of being a Windows-free household.

cheers,
Scott

[dontremember]

Michael, I've seen bleachcalc and wanted to give it a try (sounds great), but I guess that's one of the (few) drawbacks of being a Windows-free household.

BleachCalc runs just fine in Linux with wine-0.9.11. Dunno about non-x86 systems, though...

Ralph

[PoolDoc]

Hi Scott;

Given that you have extremely high CYA and 7 year old water, I'd definitely go with water replacment. 'Used' pool water does build up residue which tends to make it harder to work with -- things like phosphates, nitrates, and who knows what else.

It's this residue that is behind some of the push to measure TDS, despite the fact that TDS meters (really, conductivity meters) can't distinguish bad 'residue' from benign ionic content, like salt.

Replace as much as you can at one time -- you won't get nearly the effect from replacing 25% 2x as you will from replacing 50% one time.

But, you've got to be safe and draining your pool can definitely destroy it, depending on type and situation.

Ben

[geoeremite]

Thanks Ben. I've already completed one drain/refill cycle and am midway through the second. Drained off about 28", which I'm estimating is about 40% by volume (funny how that works). Drains pretty slow since the waste valve is a standard hose bib and there are no valves in the pump/filter/heater area that can be used to force more water to waste (would have gone faster before cleaning my filter when the back pressure was 35psi rather than 14, ).

I figure 4 passes like this and I should be in good shape. I did verify that my CYA dropped to around 150-175 after the first cycle.

[geoeremite]

Four passes later, it looks like everything is in good shape. Here's the numbers:

FC 5.0
TC 5.0
Ph 7.2
TA 100-110
CH 200-225
CYA 20-30
TDS 400

(Pool store numbers that match the values I was able to independently measure, including FC,CC,CYA.) CYA could come up a hair, but I think that I'm not going to worry about it for a bit. Was glad to see that it held its FC overnight without issue.

[aylad]

Good job, you've obviously done your homework and have a great handle on your pool. Happy swimming!!

Janet