Opened pool, CYA has gone

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BrainsOnToast

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May 29, 2015
2
Easton
I had 50-60 ppm of CYA in the pool last year when closing; drained maybe 1/6 of the pool so was expecting to open with 50ppm. I've opened this year to 0. I double checked my method and my reagents with the 50ppm calibrated sample from tftestkits and it's definitely gone.

I'm going to use dichlor to raise the CYA level as I'm currently SLAMming with bleach, but dichlor will work just as well and will also give me pretty instant CYA.

Any thoughts about this process? IIRC CYA isn't supposed to just "disappear" without draining all the water and starting again, so I guess something has used it up, but I've no idea what.

Any opinions on a better method to SLAM and increase CYA at the same time than dichlor?
 
Welcome to TFP!

CYA disappearing over the winter is pretty common. Using dichlor or trichlor at the beginning of the year is a good plan.
 
Your dichlor process is just fine. You know how much CYA it adds so be cautious.

Often, CYA will return to 0...most often, it seems, in a covered, winterized pool. No harm done except the CYA "got gone" and you will need more.
 
CYA dropping to 0 over the winter often means there is ammonia in the pool requiring a lot of FC.

I would not add any CYA until you verify you do not have an ammonia problem.
 
It looks like I had a little CYA, just not enough to register on the test; I added 6lbs of powdered CYA (most cost-effective - $30 - thing the pool store had; I'm not paying $18 per 2 lbs of dichlor!) and that should have put me up to 30 ppm; the test is now registering 40-ish ppm. FC is stabilizing better during the day and SLAM is continuing.

From reading on here, CYA "doesn't disappear" but if people see that regularly, maybe this should be mentioned that CYA can disappear, especially over winter, and that you should test it once your water is clear enough from opening?
 
He has a point, though - it is frequently asserted here that the only way to get rid of CYA is to drain.
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Well, it is. You may attempt to lose the CYA through "winter consumption", but TFP has no idea what triggers that. It may get gone and it may not.

So, we still have to say the only reliable way is to drain. TFP has no explanation why it goes away and no idea how to stop it from becoming zero.

In time, we will have a better handle on this. Years ago, we thought it was a complete oddity and treated it as such. Now, through anecdotal reports of our members, we are learning it is not quite the oddity we thought.
 

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Often when bacteria consumes CYA it converts it to ammonia which requires huge amounts of chlorine/bleach to oxidize. Dozens of gallons in a couple of days just to get the FC to hold at all. Has to be cheaper and more reliable to drain than it would be to try to induce bacterial CYA consumption.

From joyfulnoise recently,
Every 10ppm of CYA converts in ~3ppm ammonia. It then takes 10 times as much chlorine to neutralize the ammonia. So 100pm of CYA degraded would create 30ppm of ammonia which would take over 300ppm worth of chlorine to neutralize. That's roughly 62 gallons of 8.25% bleach in an 18,000 gallon swimming pool. At a cost of ~$3/gallon, you'd be looking at over $180 in bleach.
 
Ok, it should be noted that there are two ways for CYA to degrade - bacterial conversion to ammonia & nitrates AND chlorine oxidation.

Chlorine oxidation is often too slow to really matter unless you have a pool that is open all year round and the water stays relatively warm. Hot tubs typically suffer from this type of CYA loss as their temperatures are higher and chlorine levels are sometimes spiked quite high given their small volumes.

Bacterial conversion to ammonia can happen if the correct bacteria type is present. Ammonia can then be utilized by other bacterial species and algae as an alternate energy source. The end product is the conversion of ammonia to nitrates/nitrites. There are even bacterial species that will further degrade nitrates and nitrites into nitrogen gas.

However, while the biological conversion of CYA into ammonia is understood in the context of a laboratory Petri dish, it is not obvious or easily specified on how this process plays out in over-wintered pool water. Many environmental and pool care practices can affect this process so there is absolutely no way, a priori, to know if you will lose CYA or not. Because if this, TFP does not mention this as there is no certain way to know. Information like this is usually found in old threads that any user can find just by typing in some simple search terms.
 
alben said:
The top line on the test vial is 20 ppm.
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Regardless is 20 or 30. The concept still the same. If you fill the vial and still see the black dot, you don't know if you are at 0 or slightly greater.

This whole bacterial derogation into ammonia causing loss of Cyanuric Acid is news to me. I am glad to finally read this concept as it always perplexed me how much CYA I have to add every year despite only taking about 6-7" of water off the pool.

No matter how clean I close my pool and despite that I have a safety solid cover, the deepest point of the pool is always loaded with dead earth worms come the spring. After reading above, I am now theorizing that this is a major cause of bacteria in the pool over the winter. Would you guys agree?
 
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