High CYA, stubborn low FC, mild algae puzzle

[epearce]

I've been reading the forums on algae, CYA, and FC... and frankly, I have a puzzle.

After finally letting my pool guy go, who had been dosing the pool with 3 tri-chor tabs in the skimmer every week, and telling me my water was "all locked up", and needed a compete drain, I went to Leslie. Seemed like a good plan. The basics were moderate green algae, pH 6.8, FC 0, and a (probably incorrect CYA of 50), they had me shock the pool with 4 lbs of di-chor, reinforced with another 2 lbs over the next 48 hours.

Now, about a month later, and after learning the bad effects of di-chor, and tri-chor on my pH and CYA, I'm trying to go to BBB.

The short story is the pH is recovered, now 7.6. I've backwashed 500 gal a day and refilled daily for two to three weeks, about 50% of the total volume, which should have also reduced the total dissolved solids from 1900 to about 1100.

Now the puzzle.... my CYA appears to be ~300 ppm (by a Taylor K-2006 "dot" test with a 5x dilution, confirmed by Aquachek strips). I have a backwash model, and that would suggest I had a CYA of 510 ppm at end of the Leslie di-Chor shock and 6 months of tri-chor tabs. (Leslie tested CYA of 50 before the shock, and 150 after???)

But... I cannot maintain a FC of more than 3-4, even adding a gallon of 8% bleach every day. TAC is also 3-4. I have a chlorine loss of ~2 ppm/day (Tucson, sun, wind). Despite the high CYA and low FC, I only have very mild algae, visible as a subtle cloud ahead of the brush daily. Overall, the water looks great, is clear, and quite pleasant.

So, with such a low FC and high CYA, why is the algae reasonably under control?
And, why can't I establish and maintain a higher FC?
Should I continue the daily backwash, which would take to the end of July to get to a good CYA level? Try bio-active? Just live with the high CYA and low FC and wait for winter?

BTW, I'm on a well, and in a desert. A complete drain and refill is not really an option, 500 gals a day is about all the well, and the wash where the pool backwashes will take.

 

[Flying Tivo]

You cant maintain a high FC because the algae is consuming it. We dont test for Total dissolved solids. You need to stop going to the Pool $tore. They are the ones that got you to this stage. You really need to keep draining to get the CYA under control. Does not need to be backwash, you can just drain to waste. Its better to do a big drain that small drains. You can drain big and keep a sprinkler inside to wet the sides so the plaster does not crack.

good luck
Felipe

 

[Donldson]

Welcome to TFP!

A few quick to-the-point answers:

So, with such a low FC and high CYA, why is the algae reasonably under control?
Luck mostly. Could be low phosphates, metals in the water (possibly silver from the frog) or another algaecide, or any number of things. But, "mild algae" doesn't exist in a TFPC pool, you either have algae or you don't. You have algae.

And, why can't I establish and maintain a higher FC?
Because you aren't adding more. If your CYA is 300 frankly you should be maintaining about 25 FC. Which means adding more than a gallon of chlorine.

Should I continue the daily backwash, which would take to the end of July to get to a good CYA level?If that is the fastest way, yes. Try bio-active?Nope Just live with the high CYA and low FC and wait for winter?Not if you can do it faster

 

[epearce]

Thanks for the replies... I'd like to get some more thoughts on algaecide...

First an update... I believe (another Leslie test, that my phosphates are 100, its always 100) but I doubt I lave low phosphates inhibiting the algae. Also, the Frog has been unused for months, and I assume its a clean empty cartridge in there and would be surprised if it is adding metals to inhibit the algae (should I remove it?). I am a bit skeptical of these very high FC levels needed at high CYA levels as I see the difference in the algae even at a FC of 4.

I also got the FC up to 4.5 (Taylor FAS-DPD test), with CC < 0.5. I'm doing an overnight FC loss test tonight, but based on poolmath, I'd guess I am losing 2-3 FC a day. I'll know tomorrow. The algae is still just a hint of a cloud in front of the brush in the morning sweep, with nothing visible without brushing.

So, while I am working the CYA down 4% of the time with the incremental backwashes (remember, I'm on a shared well)...

1) Why not use Polyquat-60 to help manage the algae until I get the CYA back to something reasonable (recall its ~290 now, should be near 100 by the end of June)?
2) Why not try a bio-active CYA reducer to hurry the CYA reduction along?

 

[Richard320]

1) Why not use Polyquat-60 to help manage the algae until I get the CYA back to something reasonable (recall its ~290 now, should be near 100 by the end of June)?
2) Why not try a bio-active CYA reducer to hurry the CYA reduction along?

1) Algaecides work better as a preventative than as a cure in the same way that Lysol stops the spread of germs but drinking it won't cure a cold.
2) Bioactive hasn't worked as well as we all hoped it would when it was introduced. Use the search box for Bioactive and read all about it. Most likely it will be sixty bucks wasted. Check the instructions

"If pool has significant algae or organic matter, this must be removed before starting treatment."​

 

[adeleincali]

I am new as well, and no expert. However Richard320 suggested to me when my CYA was over 250 and needed to drain, to check out "Reverse Osmosis". Basically, a company comes to your home with a truck and it filters all the pool water over say a 24 hour period, removing ALL contaminants. It is somewhat spendy, but perhaps not when considering the cost of a drain or maintaining high levels of FC or extensive SLAMing. There are a few companies that do it here is SoCal. I would guess due to the water in AZ, you should have some companies as well.

Good Luck!

 

[dariushd]

1) Algaecides work better as a preventative than as a cure in the same way that Lysol stops the spread of germs but drinking it won't cure a cold.
2) Bioactive hasn't worked as well as we all hoped it would when it was introduced. Use the search box for Bioactive and read all about it. Most likely it will be sixty bucks wasted. Check the instructions

"If pool has significant algae or organic matter, this must be removed before starting treatment."​

How do you test for how much algae/organics are in your water?