Stabilizer Mystery

[PoolDoc]

"24 hours later, a Color-match DPD is registering 2.0ppm FC and 3.0ppm TC. An OTO test was WAY OFF the SCALE yellow. So I think the DPD is being influenced by HIGH chlorine, and in fact I still have chlorine after 24 hours."

If you are describing these results accurately, you were measuring a pool with low FC and high CC. And, yes, high CC seems (sometimes) to show up as FC.

I've never known CYA to be metabolized that rapidly, but then I have no really info on just how fast it can be metabolized. But, it sounds like you've got an algae/bacterial soup that's eating your stabilizer (and turning it into ammonia) as fast as you can add it. My original recommendation (borax to 7.8 & 3 gallons of bleach each and every PM) was almost certainly the right thing for you to do. It certainly would help you resolve your green goo.

It doesn't sound like you've done that consistently.

Messing around with the CYA, TA, & CH now is more of a distraction, than an aid. You need to get the goo (and probably, the ammonia pooped out by the CYA eating bacteria) dealt with first, BEFORE you worry with the other stuff.

If you want to really understand, read Chem_Geek's articles. Otherwise, just do it.

Ben

[TonyPH12345]

Ben, I've given up on the DPD test. I'm measuring whatever the OTO test measures... Isn't that TOTAL chlorine? Ordered me a replacement K2006 since my previous one is "expired" and I'm out of FAS-DPD powder anyway.

At any rate, this AM I'm seeing OTO test off the scale again (water is almost brownish yellow after adding 5 drops).

Through this whole time, my attached SPA has not had a trace of algae in it. It was crystal clear and snow white as I wish my pool were... Odd, huh? But now it is developing what looks like metal stains...brownish orange deposits on the plaster... I've had that happen before and know how to deal with that, but I'm not going to touch that until this is resolved.

The "Algae" deposits are turning grey, and they're becoming easier to brush away. But what's under the brushed spots is not clean plaster... It's still green underneath. Other than adding this turbidity through brushing, the water is clear. So all the algae is clinging algae, not water-borne.

So right now I don't have a reliable way of measuring FC. In the mean time, if my math is right and I can assume the bleach is actually 6%, adding 3 gallons of bleach to 9000 gallons of water should raise FC by 20ppm, is that right?

Thanks, ya'll, for the hand-holding. We're only about 3 to 4 weeks away from Swim Season here in Dallas, and I'm sure hoping I don't disappoint my kids.

[PoolDoc]

If you've got 3 weeks, and your filter is functioning reasonably well, you should be fine.

Grey is dead; green is live. (tho, I think you'd worked that one out ;-)

RAISE THE PH!

Adding chlorine to ammonia in a HIGH ph solution produces monochloramine, which is GOOD at penetrating clinging algae. Free chlorine is not. Monochlor is what Yellow OUT leads to, IF you follow the directions. It does work; it just leaves a mess to clean up. But you've ALREADY got the mess, so no worries there.

But, if you don't raise the pH, you'll tend to produce di- and tri- chloramines which are stinkier and are NOT good for anything that I'm aware of.

20 ppm is about right. If you brush and stuff, it will drop very quickly. But, you should probably stay out of the "brown" OTO range. I think 20 is dark dark orange.

Ben

[CarlD]

I think I see something: Your CYA didn't rise because it takes 48 hours to a week for the CYA to dissolve properly...and if you've been vacuuming to waste you may WELL have vacuumed up and out the undissolved CYA particles.

You've got a gunite pool. If it were me, I'd get a 5 gallon carboy of 12.5% liquid chlorine and dump in 2.5 gallons. That should raise the FC by about 30ppm, which may just make a dent in the algae. 8 hours later, I'd check FC again, and if it dropped, I'd dump in the rest of the LC. Gunite/concrete/plaster can tolerate such high levels, unlike vinyl.

When you use the OTO, are you diluting it with steam distilled water? If not, look up the Shot Glass method. Mix one shot of pool water with one shot of distilled, and you can double the readings. Two shots of distilled to one shot of pool water and you can triple the reading. 3 shots distilled, quadruple. Beyond that you will probably be losing accuracy.

[TonyPH12345]

CarlD: Walmart is less than 300 yards away from my front door. 1.5 Gallon bottles of 6% bleach at $2.00 per bottle is a lot more convenient than to find a 5 gallon carboy of 12.5%

My filter doesn't have a setting for Vac-to-Drain; it still recirculates. So I don't think that's where my CYA went...

Thanks for the suggestion!!

[PoolDoc]

Tony, you're right to remember that high chlorine affects phenol red . . . and in spite of having warned about that many times, I was forgetting it. But I lucked out, and still gave good advice. High chlorine makes pH appear high, not low. If you are still reading low, (7.6) I think it's prudent to assume you are.

In any case, the higher the pH, the greater the propensity to form monochloramine preferentially over other species. (So, add borax!)

Ben

[chem geek]

In any case, the higher the pH, the greater the propensity to form monochloramine preferentially over other species. (So, add borax!)

Just FYI: monochloramine forms almost immediately (in less than a minute in pools with recommended FC/CYA amounts) when chlorine combines with ammonia and this happens at all pH levels. Higher pH levels tend to produce more trihalomethanes (e.g. chloroform) when chlorine oxidizes some organics (those that have or end up with methyl ketone groups) while lower pH levels tend to produce more nitrogen trichloride from multiple substitution with ammonia and partial oxidation of urea (i.e. it is a disinfection by-product). Generally speaking, at the low active chlorine levels in pools with CYA and the low bather-loads in residential pools, I wouldn't worry about either.

[TonyPH12345]

Yeah, I didn't mention that. I'm titrating the pH up to 8.0; I've never used Borax as pH increaser before; only used Soda Ash before. So I don't know what the dosing should be and I don't want to over-shoot it...

Does high chlorine affect Phenol Red test? IOW, can I trust what I'm seeing on the Ph test when my chlorine > 15?