Algae Issues

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Loren42

Active member
Aug 1, 2022
30
Florida Space Coast
Greetings,

Looking to get rid of recurrent algae. It looks like mustard algae. Pool water is crystal clear, but keep getting algae on the walls and floors.

I've been through repeated shocks and super shocks with algaecides (Yellow ut, Green-to-Clean, & oxyethelene ethelene dichloride), throwing all equipment in the pool, scrubbing walls and floors and the algae returns 3 to 5 days later. This has been going on for the last 6 months.

I believe the cause is high CYA. It is over 100. There doesn't seem to be a reliable test for levels that high. Best guess is that it is around 150 ppm. I'd remove/replace water, but there is a problem there. We have well water and well issues.

We looked into having fresh water brought in, but the volume of water we would need would cost us about $1500, maybe more to get CYA levels at half the current value. Not a great option. The CYA levels are due to using tablets—our fault. We are using liquid chlorine now.

We have been considering augmenting the chlorine with UV-C (i.e., Delta E-46) as a way to mitigate some of the disinfectant load and slowly, over time, drain off water and refill with the well (once the well gets fixed). It takes hours to fill an inch or two in the pool and it taxes both the well and the pump.

Appreciate any thoughts or observations.

• Pool is a vinyl-lined in-ground pool, 20,000 gallons, screened-in
• Filter is a Pentair Quad DE
• Pump is Pentair Intelliflow
• Flow rate is set at 45 GPM
• Pump on-time is 11 hours per day
• Bathing load, very low
 
Just joined to learn more about pool care as things have gone whacky this year.

We've had our pool for 15 years, an in-ground vinyl-lined 20,000 gallon, screened-in pool. 14 of those years have been pretty easy to maintain, so no big worries.

Look forward to learning more.

Here's the basics.

• Just switched to liquid chlorine as our CYA is ~150
• Filter is a Pentair Quad DE
• Pump is Pentair Intelliflow
• Flow rate is set at 45 GPM
• Pump on-time is 11 hours per day
• Bathing load, very low
 
I combined your posts as folks will be asking questions about your pool details.

You live in Florida. Unless your pool is inside a room, not just a screen enclosure you get plenty of UV from the sun.

The questions you didn't answer -

-How do you test your water?

-What is your full testing look like?

FC

CC

pH

TA

CH

CYA

We base our pool care system on accurate testing and only adding what the pool needs, when it needs it. To do that you need your own accurate test kit. The two kits we trust because they provide reliable repeatable testing is-
-TF100 test kit.
-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.

Both of these contain teh chlorine test we need, the FAS/DPD test. If you don't have one of these two kits please don't go to your local pool store for a test kit. To effectively practice the TFPC methods, the FAS/DPD chlorine test is essential, and very few other kits have this test. The kits sold at the pool store generally won't won't cut it, but be careful pool store employees are known to say “it's the same thing”. Generally it's not!

As you have discovered, 100 is the limit of the CYA test, so you have to do a diluted test. While the full instructions are in the Pool School, here is the short version. Mix 50% pool water with 50% tap water. Use this mixed sample as your test water. If still at a 100 you will need to dilute more. The problem is that when doing a diluted test not only do you multiply the rage of the test you multiply the error rate of the test, so results are a ballpark - not an absolute. Here is a great chart by JamesW to explain dilution rates and what you multiply the results by to get an approximation of your CYA level.

Pool water......Tap or distilled water.........Multiply result by

....1...................1................................2
....1...................2................................3
....1...................4................................5
 
I have the Taylor 2005 and 2006 FAS-DPD test kits. I use the R-0001 and R-0002 reagents from the 2005 kit for Chlorine measurements. Not a good idea?

I can order larger bottles of regents. I figured the smaller ones would be better because they get used up faster and I don't need to worry about shelf life. Am I wrong?

I'll try the dilution test and get back to you with CYA results shortly.

Current status of pool

Free Chlorine ~3 (note: I just added another 64 oz after testing this morning)
Total Chlorine ~3
pH ~7.6
TA ~120 ppm
CH ~100 ppm
CYA > 100 (estimate 150)

Algae now beginning to return after last shock and algaecide treatment.
 
You say you have FAS DPD == use that for FC measurements. The R0870 powder and R0871 reagent.

The R0001 and R0002 are DPD reagents. That is fine for daily FC measurements when just checking to see that you have chlorine in the water. Not for accuracy.
 
I had to dilute the pool water with distilled water 1:3 to get a reading of 50 on the scale. That translates to a CYA of about 150.

Now, my understanding about UV-C is that a wavelength of 264 nm is the desired wavelength to kill algae. The spectrum of sunlight at sea level at this wavelength is almost nil.

From Wikipedia: Ultraviolet C or (UVC) range, which spans a range of 100 to 280 nm. The term ultraviolet refers to the fact that the radiation is at higher frequency than violet light (and, hence, also invisible to the human eye). Due to absorption by the atmosphere very little reaches Earth's surface.

The performance of the Delta E-46 is claimed to be 30 mJ/cm². Not sure about the translation to the graph, but the point is that very little UV-C reaches the ground due to atmospheric absorption.

1659364590687.png
 
11 hours at 45GPM through a DE Filter with algae is likely costing you a pretty penny in electricity. I run about half that speed with no issues. Perhaps consider lowering your pump speed to gain more efficiency, and use that $$ to pay for the water exchange.

You have too little FC and too much CYA. There's no magic fix - I wish there were! Water replacement and lowering the CYA will allow you to follow the SLAM process to rid the pool of algae. Then it's simply managing FC against the CYA in pool that allows for the "trouble free" aspect prescribed on this site.

www.troublefreepool.com

The Free Chlorine and Cyanuric Acid Relationship

Managing your cyanuric acid and Free Chlorine levels is key to stabilizing your pool. Learn how these two items affect each other.
www.troublefreepool.com www.troublefreepool.com
 
Stop worrying about UV and get chlorine in the pool. You could put five of these UV units on your pool and they will not help. You have already said, the algae is attached ot the side of the pool, it will never go through the UV chamber to get killed.

You have too much CYA and too little FC

You need to lower the CYA

You need to increase the FC and keep it there.

Your solution is chlorine, not UV or algecide.
 

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Loren42 said:
How will such high chlorine levels affect the vinyl liner?
Click to expand...
They won't. CYA inhibits the ability of chlorine ot do it's thing, that is why you low chlorine is not killing algae. This is your whole problem.

How much Pool School have you read? Start with these:

ABCs of Water Chemistry

Recommended Pool Chemicals

How to Chlorinate Your Pool



So, welcome to TFP!!
Loren42 said:
By the way—beautiful GSD!
Click to expand...
Thanks, That was our big boy Niko. We sadly lost him ot an aggressive cancer.


Here is our current guy, TriggerTriggerPool.jpg
 
The CYA will inhibit any damage to the liner? My wife s just worried.

The well is drawing sand. Unfortunatelly, all the well services here have a huge backlog or 3 to 6 months already (probably due to the housing boom we have). We can't connect to city water becuase it would be expensive to have the water routed to our street and our underground house pipes are of a plastic that has known issues with chlorine, so I don't want to rip up our slab!

We can live with changing out the sediment filter for now, but filling a pool with high rust and sulfur well water is bad for both pool and well.

Likewise with our dog, but ours was a progressive stenosis of the spine. She was a real brat, but we loved her just the same. Now we have a 5-1/2 month old Collie. :) Can't live without a dog.
 
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