Black Algae and results of first tests - where to begin?

[keith131]

Hi all,

I could use some help with our pool issues. It appears we have black algae and I believe I understand the SLAM process, but in light of my apparent CH problem, I am at a loss as to where to start and in what order to address our issues.
Here are my first try at test results with the K-2006 test kit. I ran them in duplicate. Just for reference and in the interest of full disclosure, I ran water over to the local Leslie's (used over the last five years until now - results are as of 8/5)

FC = 1.8, 2.0 (first method was .2ppm per drop, second was 0.5ppm per drop) -- L 0.92
CC = 1.8, 2.0 -- L 1.19
pH = 8+, 8+ -- L 8.1
TA = 80, 80 (a very pale red after 7 drops in both cases) -- L 68
CH = 950, 875 -- L 491
CYA = <30, <30 -- L 15
Salt (if applicable) = Cell indicates low salt. -- L 3488

The CH test was the main reason I ran everything twice. I wasn't sure I was doing it correctly (35 and 38 drops with the 10 mL sample volume method).
My wife attempted to scrub the algae, but was only able to remove the surface, consistent with what's been described here.
I haven't delved into the operation of the SWG, thinking I'd do that as I addressed other issues.
One of the attached pictures shows white material sitting on the bottom of the pool. Is that salt or some other material?

Any assistance you can provide to get us back on track is greatly appreciated. I just don't know the order in which these issues should be addressed. I am picking up a stainless steel brush and liquid chlorine this morning and will pick up other needed supplies as suggested. Do I need to bring up my CYA first, so is stabilizer on the list as well?

Thanks for you help,

Keith

 

[Texas Splash]

Hello Keith and welcome to TFP! So you have a delima ... local hard water, algae, and potential calcium build-up. To kill and remove algae, we follow the SLAM Process, but before that you have to determine if you can exchange some water to try and lower the CH level a bit. Once your CH gets over 800, things get a bit tricky to manage. So here are a couple options:
1. Try to do a good water exchange first - maybe half or so if you can (quickly) to avoid leaving the pebble exposed to the hot sun too long. If you are able to do that and lower the CH a bit, then you should be able to manage your overall levels better to prevent scale. After the exchange, you could also begin the SLAM Process to kill the algae.

2. Leave the CH alone for now and go right into the SLAM Process. Once the SLAM is complete, you'll need to maintain a much lower pH to help compensate for the elevated CH level. The PoolMath APP is what we use and is a great tool to help with that. With a CH close to 900, you'll want to keep the TA around 60-70 and the pH around 7.3-7.4 which should keep the "CSI" at a slightly negative range which is perfect.

Many in your area wait until winter to do their water exchanges to avoid sun damage to their plaster, but it's up to you. But the SLAM Process is where you need to start for the algae. The link below should also help. Let us know if you have any questions.

Black Algae

This guide provides a step by step procedure for eliminating black algae in your concrete or gunite pool. Read full post here.

www.troublefreepool.com

 

[keith131]

Thank you, sir! Nice to hear from someone from River City.

Unless someone convinces me otherwise, I'll go with #2. The SLAM process is something I can address in the short term, with finding and maintaining a good CSI range something I can hit afterward and look at water replacement in cooler weather. I've been working on the Poolmath web page and assume the math is the same in the app and on the website. So it looks like my steps are:

1. Bring up CYA to 30 - I'll assume I'm starting with 15ppm and add 29oz of CYA in a sock to bring it up to 30ppm (or something closer to it than where I am)
2. Drop pH to 7.2 by
a. addition of 54oz of 31.45% MA, assuming my math is correct (according to my 4 drop acid demand test and MA (fl oz) = 9.165 * 1e-4 * N * V where N is the number of drops required to reach goal pH and V is the volume of the pool in gallons) or
b. do the two step, adding enough (15 oz) according to Poolmath to bring it from (assumed) 8.1 to 7.6 , hoping to bring it into measurable range to performed a second addition to bring it down to 7.2 for the slam (based on a TA of 80).
3. Remeasure CYA and FC. I will add 150oz of 12.5% liq chlorine based on my CYA of 30 (adjusting value to the actual final CYA that I obtain) to bring it up and maintain an FC of 12 until I scrub away the algae. My SWG will be off during this time.
4. Once the slam is complete, I'll watch the CSI until I can look at replacement as the weather cools down (October).

Does anyone see a problem here? My questions:

**Do I need to do it in that order?
**If the sock of CYA is completely dissolved, can I measure CYA at that time or should there be a delay?
**Is it imperative that I get my CYA up and know what it is so i can correctly calc the FC level for my SLAM?
**Can I drop pH to 7.2 as the CYA is dissolving?
**The previous person who maintained the pool was told that the pool pump should be run for 24 hours after MA addition before remeasuring. I read of much shorter times (30 minutes?) on this forum. Is there a good number i can use?
**Is the white deposit on the pool floor calcium carbonate from not maintaining the CSI slightly negative?

One "feature" that the pool now has is a ring of deposit on the tile at the water surface. My thought was to address the ring (bead blasting or coming back to TFP for a DIY solution) at the same time as the water replacement.

Thanks,

Keith