Alkalinity Zero

[sdaggie]

I am new to taking care of the chemicals in our house! I've been trying to raise my alkalinity all summer. The last readings from the pool store were:

CYA = 146
Tot Chlorine = 15
Free Chlorine = 15
pH = 7.5
Total Alk = 38
Adj Total Alk = 0

At their suggestion, I added 50 pounds of Sodium Bicarb (over 3 applications). When I test the water (using my basic Taylor kit) I cannot get my Alk to turn from green to red even after adding 40 drops.

My pool: 20x40/inground/vinyl. We are no longer swimming for the season so the heater is off and the cover is on every day.

Any help/advice is much appreciated!!!!!!!!!

[CarlD]

Hi and welcome!

Your pool store is giving you a bum steer. Is your pH stable? That's all TA does: buffers pH.

I suspect your TA is NOW through the roof, and will take far more than 40 drops to get it to turn. If your TA was very low it would turn quickly. I would NEVER add 50 # of bicarb and my pool is only slightly smaller. So now you have a potential problem to fix that was totally their fault. Question: Did THEY sell you the bicarbonate, too, telling you it was "different" than Arm&Hammer? And charge you 3x what the A&H costs? (It's the same stuff).

Meanwhile, your CYA is VERY high--too high IMHO, and they didn't bother mentioning THAT to you! Luckily your FC level is fine for that CYA for maintenance. (over 100ppm we recommend a maint level of 8-15 of FC.)

If you are using Tri-chlor tablets or Di-Chlor powder STOP NOW! They are only making your CYA situation worse. Switch to bleach/liquid chlorine. If your CH level (Calcium hardness or just hardness) is low, you can also use Calcium Hypochlorite powder. It only adds calcium.

You CAN maintain your pool with CYA there as I said but you'd do better to drain 1/2 to 2/3 of your water and refill, dropping your CYA by dilution to the 50-75 range.

That's what too many pool stores do: Create problems where there were none so they can sell you more stuff.

[sdaggie]

Thank you for responding. What I meant when I said that it I can't get the Alk to turn from green to red is that the Alk is still registering zero (the test did the same thing before I added the Sod Bicarb).

When you say the CYA is very high - my printout shows ideal is 30-200.

I use BioGuard Silk Tabs and Burn Out shock each week. I think there is stabilizer in the tabs? My Total Hardness is 276.

I don't want to drain my pool. We had to do that a few years ago and it is not good for the liner (left wrinkles).

Any other suggestions? Thanks so much!

[kelemvor]

When you test your alk, use the 10ml sample size instead of 25ml. The loss in precision will have no bearing on how you dose your pool. Also, using the smaller sample size means you save reagents and time by using less drops to achieve the color change.

[chem geek]

Testing for chlorine in a FAS-DPD test with a 10 ml sample size makes sense since 0.5 ppm resolution is usually sufficient compared to 0.2 ppm with a 25 ml sample size. Calcium Hardness (CH) is another test where one could use a 10 ml sample size for a 25 ppm resolution. However, for Total Alkalinity (TA), the resolution of 10 ppm with a 25 ml sample size is usually needed. For initial TA adjustments the smaller sample size may be OK, but when making final adjustments the 10 ppm resolution is preferable.