Black Algae and High CYA

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ChrisMP

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Jul 7, 2013
3
New member to the board . . . .any input/advise welcome.

FC 1.0, CC 0, pH 7.8, Ca H 250, TA 80, CYA 120

I have black algae starting on the steps and benches - first time for me. I have scrubbed the algae using a stainless steel brush and I just flushed the cartridges.

I normally use the jumbo tabs with conditioner due to my travel/time-demands. I know that water replacement for high conditioner is the cost of this choice.

I was going to shock the pool to eliminate the algae, but know that I need to drain the pool as well . . .. my question is - should I shock the pool first then drain the water, or drain the water, then shock? I know that I have to drain 1/2 to 2/3 of the water. Any other remedies or advice would be appreciated.

Thanks
 
Welcome to the forum. :lol: Drain first, refill and shock. You'll be able to give the black algae the old heave ho once you get it exposed.

Pretty sure you know this but black algae seems to appear most frequently in pools that have been chronically underchlorinated. Not just days or weeks, but months.

Keep that FC up probably at the very highest range of normal (actually, I would keep it 50% higher than that for a month or so) after you get refilled so it doesn't have a chance to get back....it's tough.
 
Don't forget to use a stiff brush (metal bristles are OK with a hard pool surface) to scrape off the waxy layer to expose the deeper layers of the algae to the high chlorine levels. With already established black algae, brushing is critical.
 
Thank you very much for the help. I am assuming that the under-chlorination is due to the high CYA levels? I have pretty consistently had 1.5 readings for FC with no detectable CC. I had not been regularly testing for CYA.

y_not - is there a thread on SWCG and acid pump that you would suggest? I would like to read-up on the subject as I am not really familiar with the equipment/costs/maintenance.

Thanks again for the help.
 
1.0 FC, even 1.5, is WAY TOO LOW for that CYA. I would not recommend even trying to maintain a pool with little or no CYA at that level.

How sure are you that your CYA is ONLY 120? CYA over 100 is very hard to measure and often the CYA is much higher than what the test reveals. Try mixing your pool water half/half with tap water and remeasure, then double the results.

And I'm going to restate what was said above - WIRE BRUSH. If you don't break it up, you'll never defeat black algae.
 
ChrisMP said:
y_not - is there a thread on SWCG and acid pump that you would suggest? I would like to read-up on the subject as I am not really familiar with the equipment/costs/maintenance.

Thanks again for the help.
Click to expand...

No specific thread, not really. In this case the Google search box @ top is your friend. :) They go by many names, SWCG, SWG, salt water generator, salt water chlorine generator, salt pool, etc...
Read about them in Pool School as well, see my sig or @ top right of any pg.
If that doesn't do it for you, topic search can be found @ the extreme bottom left corner of the main TFP pg. It's an itty bitty, inconspicuous link. "advanced site search"

Also, if you'd like, you can start a new thread under the SWG topic/forum to discuss SWCG options for your pool and needs.
Normally we discourage from starting separate threads, however I would think it'd be OK as It's specifically pertaining to SWCG units, of which this this thread's topic has nothing to do with. Keep your CYA and current, non SWCG related water treatment problems to this thread, inline with its topic.
But I'm not a mod, and It's ultimately up to them.
 
:wave: Welcome to TFP!!! :wave:

I think you have not yet gained an understanding of the CYA/FC relationship as shown in the Pool School. Have you read it? Specifically : pool-school/chlorine_cya_chart_shock

If your CYA was 100ppm, the MINIMUM that your FC must be to prevent any algae from starting to take hold is 7ppm ... obviously much higher than the 1.5ppm you reported. Your CYA is even higher, so your minimum FC level would be even higher.

From that chart you should be able to realize that the tablets are just not a sustainable method of chlorination. They add FC and CYA. The FC is consumed, but the CYA builds up higher requiring more FC which adds more CYA:
pool-school/types_chlorine_pool
 
ChrisMP said:
Thank you very much for the help. I am assuming that the under-chlorination is due to the high CYA levels? I have pretty consistently had 1.5 readings for FC with no detectable CC. I had not been regularly testing for CYA.
Click to expand...

As RobbieH said, that is nowhere near enough FC to keep algae at bay.
FC shares a symbiotic relationship with CYA. As in, the higher your CYA, the higher your FC has to be for proper sanitation levels.

For a CYA of 120ppm, you can't let your FC level drop below 8ppm at minimum, any given time of the day.
See extended CYA chart in Pool School @ chlorine-cya-chart-t2346.html

I would suggest you do some reading and studying in PS on how this all works.
 
Thanks for the help. I have started the drain on the pool and I have exposed the steps where the black algae was forming. I scrubbed it with a wire brush.

I will start refilling and then shock the pool.

I will definitely read up on the pool school materials (it's been a while) - especially the CYA-FC relationship

And finally, I will see about getting off the tablets and going to liquid chlorine. I'll have to make some changes to how I manage the maintenance, but hopefully this can be avoided.
 

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If you only travel occasionally, using tabs while you are gone is probably something that will work for you. But if you spend as much time away as me (50%+ travel, 4-5 days at a time), a SWG is something you should consider. With a 20k gallon pool, you might be able to get away with a Liquidator, but for me it did not have large enough capacity to maintain the pool while I was gone, and I still had to carry bleach bottles home.
 
RobbieH said:
...might be able to get away with a Liquidator, but for me it did not have a large enough capacity to maintain the pool while I was gone and I still had to carry bleach bottles home.
Click to expand...

Don't you have to carry acid bottles home too? :stirpot:
Or is it simply the lesser of the 2?
 
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