Black algae and just got Test kit and results - need guidance

[bpascente]

Hi Folks,
Per my original thread, I have fighting black algae for the past 2 summers. I have done a lot of reading on this site, purchased a recommended kit, and have my 1st test results. I am still looking for a reasonably priced liquid chlorine (so far best I can find is ~ 4.00/gallon) as I am fairly sure I will need to slam.

If someone could guide my assumptions of what I believe are my next steps, I would greatly appreciate it as I am new to the TFP process.

TEST RESULTS:

CYA >100 (Does not reach to the 1st line which is 100 - It falls about 1/8" below the 100ppm line, so I will assume a CYA of 110-120).
FC 15ppm
CC 1.5ppm
TC 16.5ppm
CH 550ppm
TA 80
PH 7.5

NEXT STEPS??

From the calculator on this site, it appears I need to replace 64% of my pool water, or about 6000 gallons. This should also help my high CH. Since I live in Phoenix, I am concerned about plaster delamination due to the warm temperature, but will remove water in the evening hours.
Retest CYA after replacing water and aim for a goal of 40-50ppm.
Retest all parameters with the assumption of starting a SLAM?
Continue brushing black algae 2x per day with SS brush.

Does this sound correct? Any tips on locating inexpensive liquid chlorine or bleech for a SLAM would be greatly appreciated!

 

[MarianParoo]

I would double-check that CYA first with a dilution test outlined in step 9 here:
Pool School - CYA

 

[bpascente]

Will do......is this because you have seen many 1st timers misinterpret the test reading?

 

[MarianParoo]

Because your CYA tests 90 or above, it is best to do a diluted test. It has nothing to do with being new. You said you are assuming that your CYA is 110-120, but that is a guess. It could be higher. The scale for CYA is logarithmic, not linear, as you can see on the test vial. e.g. Midway between 40 and 50 is not 45 but closer to 48.

The goal is to do only one drain and refill to get your CYA where you want it. Having a more accurate CYA reading will help in calculating the correct percentage to drain.

 

[bpascente]

Thank you Marian. Yes, I did notice the scale was logarithmic. It makes sense. Our tap water is highly chlorinated. Would it be better to use reverse osmosis water for the dilution test?

 

[MarianParoo]

It really doesn't matter. Neither of those sources will have any CYA in it and that's the critical part. The presence of chlorine will not affect the test. Bright daylight is the key to good results.

- - - Updated - - -

Also the directions say to mix it and then pour off half. I think it's easier to mix it, then pour it into another container, and then add back to the original container up to the bottom line. I always worry that people will pour off too much and have to keep starting over.

 

[bpascente]

For clarification, when you say "Mixing", I assume you are referring to mixing the tap and pool water, not the CYA agent?

 

[MarianParoo]

Yes.

- - - Updated - - -

Sorry for the delay. I was enjoying our crystal clear pool...!!!

Is it still real sunny in AZ for the test? Otherwise, wait until tomorrow.

 

[bpascente]

Hi Folks,
I have not posted in the past few days as a rare event of cloudy, rainy days hit the Phoenix area. However, I drained my pool 2 nights ago, gave the black algae a 10% bleach bath and scrubbing with 1 gallon and refilled the pool. I then added 1.5 cups of CYA to the skimmer (adding it slowly so I don't go over the 40 - 50ppm point). I ran the filter for its normal 3 hour cycle and tested total chlorine (over 10ppm) and PH (7.7) to make sure basic chemicals would hold it over till this AM.

TEST RESULTS 24 hours later:

CYA essentially 0 (Not even a bit of cloudiness in CYA measuring tube when completely filled).
FC 1ppm
CC .5ppm
TC 1.5ppm
CH 250ppm
TA 110
PH 7.7


Since my CYA of pool water was 0, I used a new test included in the TF-100 test kit this spring. The agent is called R-7065. It is described as essentially pool water that has a 50ppm (+/- 5%) CYA level as stated in the insert. This is to be used if you doubt the age/strength of the active test re-agent R-0013. I did not get a reading with the 50ppm pool water re-agent either. I really need to dial in the CYA of my new pool water quickly, as possible as the chlorine is being eaten up quickly (as you can read from the 24 hour refill level to now). I really need some help, but don't want to add too much more CYA. I added 1 more cup today before the filter cycle. I have contacted the company where I purchased the kit, but they referred me to an RMA person who has not yet called me.