Confused about chlorine levels & CYA

[poolnovice1]

I recently fired my 4th pool technician. The CYA was off the charts and ALK levels were extremely low. After adding some sodium bicarbonate and draining the pool I'm currently at the below levels:

- FCL: 6.87
- TCL: 9.71
- PH: 7.6
- ALY: 84
- CH: 85
- CYA: 124

Most of these are within range according to the testing system I'm using. I've read some articles about CYA and chlorine levels. Supposedly I should be using much higher chlorine levels but they're already high. Frankly I'm just confused and need some recommendations.

I have a 25,000 gallon pool. I shock 1x week (3 1lb bags) and add 2-3 chlorine tabs very other week. I live in Houston and we're about to get some very hot weather soon.

- Do I need to increase my FCL/TCL levels with my current CYA levels? Or should I just be using more shock?

 

[jblizzle]

Re: Confused about chlorine levels & CYA

Welcome to TFP!

How are you getting your test results? Those are clearly not from one of the recommended test kits.

If you choose to believe those numbers, which I would not, your cya is way too high still. And the fact that your total chlorine is so much larger than your free chlorine means that you're combined chlorine is high which is not good.

Your problem with the high cya is likely due to your continued use of powdered shock. We do not ever recommend shocking your pool with a random amount of powder every week. If you maintain the proper chlorine level for your cya, you will never get algae and never have a need to shock. If a problem does develop it then you must follow the slam process.

 

[funandsun]

Re: Confused about chlorine levels & CYA

Yeah, that CYA is crazy IF it's accurate.

https://www.troublefreepool.com/content/128-chlorine-cya-chart-slam-shock

 

[jeffchap]

Re: Confused about chlorine levels & CYA

Your FC and TC levels are not high at all when considered in comparison to your CYA. In fact, FC is too low which is going to lead to an algae outbreak very soon.

How TFP differs from the pool industry at large is that we always measure Free Chlorine (FC) in relation to CYA. To maintain healthy water, FC must stay above 7.5% of CYA at all times. If your CYA is 124, your FC needs to be at least 9.3 to keep algae at bay. You are well below that, and that fact that your Total Chlorine (TC, which is FC + CC) indicates that your Combined Chloimines (CC) is 2.84. CC should be .5 or less. That it is high indicates that something is growing in your pool and the free chlorine is struggling to kill it.

Your use of tabs and shock powder are only raising your CYA each time you add them, thereby raising in turn the FC level required to keep your water clear. This is why we recommend the use of liquid chlorine, aka bleach, to chlorinate your water. It adds no CYA to your pool.

You should discontinue the use of tabs and shock and switch to bleach ASAP. Your CYA is already too high, and that's if you trust the pool store testing. We do not. Pool stores are notoriously bad at measuring CYA. It could in fact be much higher. The only way to reduce it is to partially drain and refill your pool. How much depends upon what your true CYA level is. The optimal value is 30 for a manually chlorinated pool, meaning you need to drain and refill 75% of your water with CYA at 124. More if it's actually higher. You can manage CYA up to 80 or so -- it just takes a lot more chlorine to do so.

I would suggest you order one of the recommended test kits, either the TF-100 or the K2006 so that you will have accurate measurements to work with. Once you have that, you will need to lower your CYA to a manageable level and perform a SLAM described in our Pool School to kill the algae currently trying to take over your pool. A SLAM is simply bringing FC to 40% of CYA and keeping it there until everything is dead.

 

[poolnovice1]

Thanks. I'm afraid to put my kids in the pool with the way it is now.

The kit I'm using is LaMotte 2056 ColorQ Pro 7. Are these reliable?

So it sounds like what I need to do is drain the pool more to bring down the CYA and then add liquid chlorine. I've drained about 5,000 gallons so far.

 

[jblizzle]

Re: Confused about chlorine levels & CYA

Most people that have the color q that come to this forum end up abandoning them due to inconsistent and inaccurate results. It also has limitations such as the FC not reading high enough for high cya levels.

I'm not sure how much I would trust any of the numbers 2 determine the path forward at this point.

 

[Donldson]

I'm not a fan of the ColorQ and really I find the TC number suspect. If it is accurate you have a bigger problem than just high CYA as you have nearly 2 ppm of CC. That is indicative of a problem that needs corrected, but I would personally not take actions based off of ColorQ readings. It's built down to a price, there's no getting around that.

 

[Pollock]

I have the same color q water tester. It seems to do cya in the ballpark but nothing else.
My color q would say 7.2 ph but it was really 7.6
TA would read 80 but it was really 110.
CH said it was 200 but it was really 270.

Maybe yours is better than mine but I switched to the Taylor K 2006 C. A little more time consuming but I feel its accurate.

 

[tim5055]

Please do not confuse the specificity of the results the ColorQ gives with accuracy. We have had members attempt to use the ColorQ to follow our methods and almost all have abandoned its use due to inaccuracies and inconsistencies. We even had one member test the same sample of water three times in a row and ended up with three different sets of results. Here is an example of a ColorQ post: ColorQ vs TF100 and here is a review where the Color Q was used alongside a TF-100. Test Kit Comparison

As far as your concerns for "high" chlorine levels go, the CYA acts as a buffer to the chlorine. As long as you keep the FC in the correct ratio to CYA you are fine and the kids can swim. When my CYA was over 250 I had to keep my FC above 20 and never noticed it, again because it is bound to CYA and buffered.

Order a TF100 and at least include the XL option. That will give you what you need while you are clearing the pool, and probably enough reagents for a couple of years normal use.

The only other real option for a test kit is a Taylor K-2006-C. Be careful comparing prices because the K-2006 comes in sizes, designated by a letter. The basic K-2006 has .75oz bottles. You need to get the K-2006-C to get the larger bottles that you want. Even then it is a little short on the reagent & powder for the FAS/DPD test.