Unexplained CYA increase?!?

[Kfrey]

My CYA was 70 this week during a SLAM I was doing. Chlorine source was 6% chlorine bleach... that is it! It rained very hard after I finished the SLAM. I gained a lot of water in the pool that day. The next day I went back to vacuum and check levels.... CYA went from 70-100! After a rain storm! Only chlorine source was bleach.???

 

[mknauss]

CYA only increases if you add it. No natural sources.

Most likely testing error. Read Pool School - CYA

 

[ajw22]

If your CYA is possibly that high you should redo the test following point 8 in Pool School - CYA

8. If your CYA level is 90 or higher, repeat the test adjusting the procedure as follows:

Fill the mixing bottle to the lower mark with pool water.
Continue filling the mixing bottle to the upper mark with tap water.
Shake briefly to mix.
Pour off half of the contents of the mixing bottle, so it is again filled to the lower mark.
Continue the test normally from step 2, but multiply the final result by two.

 

[Kfrey]

CYA only increases if you add it. No natural sources.

Most likely testing error. Read Pool School - CYA

I retested and it could be closer to 90. The crazy thing is that the pool gained about 2 inches of water (30k gal pool). I know my CYA level was accurate before because I successfully completed my SLAM at CYA of 70.

 

[Kfrey]

If your CYA is possibly that high you should redo the test following point 8 in Pool School - CYA

Ok retesting using #8.... I got 45 so the actual value would be around 90.... so I guess in need to lose some water and refill?

 

[ajw22]

Ok retesting using #8.... I got 45 so the actual value would be around 90.... so I guess in need to lose some water and refill?

45 is not a meaningful CYA value. The CYA scale is logarithmic, not linear. You cannot eyeball values in between the lines. Halfway between 40 and 50 is not 45. You always need to round up and say your test showed 50 and your CYA is in the 100 range.

The actual number is meaningless at that level other than to say your CYA is very high and you should get your CYA down to 30. That means exchanging 70% of your water. Marty will likely be back here soon and can give you the best process for exchanging water in a vinyl pool.

 

[mknauss]

It would be best to get your CYA to the 50 ppm range. I am concerned that you had tested it lower in the past and now higher. Be sure the conditions (sun at back, time of day, etc) is the same.

You can drain down to leaving one foot of water remaining in the shallow end and then refill. There is risk in that if you have a very high water table. It should get you close to 50 ppm CYA.

You can exchange some water without draining.

If you place a low volume sub pump in the deep end and pull water from there while adding water in the shallow end (through a skimmer or into a bucket on a step so you lessen the water disturbance) you can do a fairly efficient exchange. That is assuming the water you are filling with is the same temperature or warmer than your pool water. If your fill water is much cooler than your pool water, then switch it. Add the water to the deep end (hose on bottom) and pull water from the top step.

The location of the pump and fill hose may change if you have salt water, high calcium, etc.
In my pool, with saltwater and high calcium when I drain, I put the pump in the deep end and hose in shallow end. The water in the pool weighs more per unit volume than the fill water from the hose.

Be sure to balance the water out and water in so the pool level stays the same. Also be sure your pool pump is disabled during this process. Once started do not stop until you have exchanged the amount of water you wish.

 

[Kfrey]

It would be best to get your CYA to the 50 ppm range. I am concerned that you had tested it lower in the past and now higher. Be sure the conditions (sun at back, time of day, etc) is the same.

You can drain down to leaving one foot of water remaining in the shallow end and then refill. There is risk in that if you have a very high water table. It should get you close to 50 ppm CYA.

You can exchange some water without draining.

If you place a low volume sub pump in the deep end and pull water from there while adding water in the shallow end (through a skimmer or into a bucket on a step so you lessen the water disturbance) you can do a fairly efficient exchange. That is assuming the water you are filling with is the same temperature or warmer than your pool water. If your fill water is much cooler than your pool water, then switch it. Add the water to the deep end (hose on bottom) and pull water from the top step.

The location of the pump and fill hose may change if you have salt water, high calcium, etc.
In my pool, with saltwater and high calcium when I drain, I put the pump in the deep end and hose in shallow end. The water in the pool weighs more per unit volume than the fill water from the hose.

Be sure to balance the water out and water in so the pool level stays the same. Also be sure your pool pump is disabled during this process. Once started do not stop until you have exchanged the amount of water you wish.

Interesting... but how do I gauge the amount of water I am removing from/ adding to my pool using this method? By timing it? I could calculate the fill rate with a bucket I guess. ??*??


30k gal in ground vinyl pool, Taylor K-2006 kit

 

[mknauss]

You are correct. Use a bucket to measure the output of the sub pump. A 1/4 or 1/3 hp sub pump using a 3/4" hose to run to your sewer cleanout normally will run at 4-7 gpm. So you run the hose into a 5 gallon bucket to start and time it. You then can get the flowrate.

 

[Spa Owner]

Be interesting to take say six samples from the pool at different points and different depths and see if you notice a large difference in readings. Getting a low reading and then a high reading after rain may indicate a circulation issue.