Measuring CYA when above 100

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M

markmac

0
Jun 29, 2011
183
Texas
I've purchased a home with a pool. I have no expereince with pools and am trying to understand the chemistry as fast as possible.

The water looks fine, and as far as I can tell seems fine. However the test results have me confused as to whether I need to do anything. Specifically, the CYA is apparently very high and I'm not clear on what that hurts.

When I purchased the house, there was an Chlorine floater in the pool with two old pucks, and a new puck in the skimmer. I had a note on the door from the previous pool guy who stated he adjusted the chemicals and wanted to know if we wanted to continue with his service. I figure I'll give it a shot and see if I need any help later. However the more I look into it, check the baskets, and general status of the pool, I donlt think he was doing more than dropping a puck in teh skimmer eveyr week or two.

I purchased the suggeested K-2006 test kit and also had Leslies test the water. Here are the current results;

FC 5
CC 0
TC 5
PH 7.4
TA 130
CYA <100 (in the test, I cannot even get close to the 100 line. A couple drops and the dot is gone)
TDS 1250
Phosphates 1000

As you can see the CYA is high, and my FC seems low for that level of CYA according to the charts here, if I understand correctly. However, I have been checking every day during the last two weeks (since owning) and the CC is unchanged. FC has gone from 4-7 when I added bleech once, one week after purchase. A week later and its only back to FC5 and CC still 0.

As I said, the water seems clear, the pool seems clean. The only item I can comment on is there are various spots on the plaster, but they don't seem to be alge, but I'm not sure. They don't rub off, and I'm wondering if its just the plaster showing its age. There is also a small amount of scale build up along the edge.

When I read the shock page, it seems like my FC is very low and I should be raising it significantly. However it does not seem to be changeing, and from what I can tell, I don't really have any issue, do I?

Do I need to urgently do anything? Lower CYA? Raise FC? Shock?
 
Welcome to TFP!

I would go ahead and deal with the high CYA before doing anything else. By lowering the CYA, it will be easier to shock the pool because you won't need so much chlorine. Go ahead and replace 1/2 of your water, retest the CYA, and go from there. You know it is at least 100, but it is probably more. Doing a 50% replacement will hopefully get you below 100.

Ignore the TDS and phosphate levels. They are not important. What is your calcium hardness (CH)?
 
To take a reading that is past 100 (unmeasurable), fill your test vial with only 1/2 of your pool water. Fill the remaining 1/2 with distilled water. This results in a mixture of 50%/50%. Then do your CYA test. Take the reading you get and double it, to derive your true reading.

This is better than emptying the pool 1/2 ways and retesting with a chance of not being low enough. Or you could do as what seems to be happening to me, wait it out over the winter, and the CYA "magically" disappears.
 
It makes your pool difficult to manage. If your CYA is 150, you should be keeping FC probably up around 15+ to be effective....notice the charts don't go above 100.

If you ever need to shock, you will have to back up a tanker truck loaded with chlorine to do so successfully.

In a nutshell, CYA can reduce the EFFECTIVENESS of chlorine to a point where it is difficult to maintain a sanitized pool.

Easily, it is the most common water quality issue posted on this forum.
 
In San Diego you should have R/O (reverse osmosis) available to you and with a CH of 600 I would seriously look into it. It will remove the CYA and the CH (along with everything else). And the people doing it will rebalance your water so you're starting from a good place.
 
Markmac, you've got some of the same problems as me ... high CH and high CYA. Before going overboard on this, are you OK with how the pool water is right now? If yes, do what I'm doing (suggested by Richard320).
Buy a sump pump and use the pool water to water your lawn. I bought one from Lowes for $88 that I can hook up my garden hose to.
I shut off my auto fill and when the water gets a bit low, I water all of the plants in the yard. I never let the water level get below the tile because the low temp here at night's ~80 (too hot to get the plaster exposed to air). Once I'm done watering, I refill the pool with soft water. You can refill with regular tap water if you want; either method will lower your CYA the same amount. I use soft water because my CH started at 980 and the tap water CH is 240.
Over the course of time, both your CYA and CH will decrease.

If you choose to go the reverse osmosis route, a company will come with a big 'ol truck and reverse osmosis your pool water until the CYA and CH levels are lower. The sump pump solution will also get you there - it's a slower but cheaper route.
 

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Jason, that's true only if you dump the old pool water down the sewer system. The beauty of Richard320's idea is that you no longer need to use tap water to water your lawn/plants - you use old pool water. So there is near zero waste of water by doing this. The costs to the pool owner are the sump pump, electricity, and the man hours required to manually water the lawn.
... there is one additional cost for me. Rather than put sodium chloride treated soft water in my pool, I'm putting soft water that has been treated with potassium chloride. Potassium chloride water softener pellets are ~ 3 1/2 times as expensive as sodium chloride but potassium chloride is considered a plant fertilizer while putting a lot of sodium on plants isn't a good thing. Morton's Potassium Chloride is $13.44/40lb bag vs $3.88/40lb bag at my local Walmart.

My wife was very happy about me using old pool water to water the plants because she now feels that the pool is 'cleaner' because the old water is being replaced by fresh water.
 
Today I noticed some yellow sludge around the skimmer. When I rubbed, it plumed yellow. I assume alge?

When I did the 50/50 pool/distilled water, my CYA measures 100, so doubling is 200 ppm.

Obviously I need to do something to get the CYA down, and I'll likely try draining before RO. It's approx $400-$500 for RO, and only $250 to refill the entire pool.

I didn't want to let the alge get ahead of me, so I dumped loads of bleech in. The FC is +50ppm which is pretty high, but its likely not even shock level from what I can see with my high CYA.

The pool is an odd shape, so best I can calculate, its somewhere around 25k gal. If my logic is right, to get from 200 ppm to 50ppm in CYA, I need to drain 3/4 of the pool and refill?
 
It depends on where the ground water table is. If your ground tends to get swampy and water saturated, it might be best to only lower the water in the pool a little several times. If you live in an extremely dry arid area then you are totally fine. For areas that are somewhere in between, it is probably alright to drain that far, but it is difficult to be sure without local knowledge of where the water table tends to be.
 
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