Black Algae in saltwater pool

Looking for useful information on how to remove Black Algae and then maintain to keep clear. Problem appeared 4 years ago but was solved by a service, but long since forgotten how. Posting here as new user, although I know similar posts already exist. Thanks.
28,000 gal saltwater pool 8 years old
Use about 120-180 lbs salt / month in summer to keep level about 3,200 ppm after adding depending upon weather and usage
PH 7.3
Chlorine 4.5 - just shocked using Leslies granular high dose chlorine shock
Stabilizer 65 ppm
No Calcium level - but finding out
Added stabilizer and algaecide pre-season - per direction on containers
Pool was "shut down" for 3.1/2 months Dec-Feb - due to ice storm cracking pipes and heater element following pump failure during absence - typical bad timing. Therefore pool was not consistently balanced for almost 4 months.

Here is my current plan;
1. regular (daily is all I can muster) scrubbing w/ss brush
2. Turn up Chlorine to 4+ ?? ppm via adding chlorine in addition to chlorinator boost
3. Add Muriatic Acid - 3 gal
4. Incorporate the "Borax" plan to prevent future algae (of any colour) breakouts.

Do I need to add an algaecide or do something differently or in a different order?

Thanks

Bad plan! Sorry, but I gotta be honest.
1) with black algae and a serious bloom, all you'll do is shorten the life of you salt cell by pushing it into boost mode. Instead use bleach or liquid chlorine to raise Free Chlorine level. If your Calcium level is low, you can also use Cal-hypo to chlorinate. Calcium levels are irrelevant in vinyl pools but need to be maintained between 200 and 400ppm in concrete/plaster/tile type pools.
2) with your pH at 7.3 why are you adding acid?
3) The ONLY algaecide we recommend is Polyquat 60%. If the bottle says "Poly...<something unpronounceable and long>.. 60%" and nothing else, that's the stuff. The rest just make things worse. Chlorine is generally the best algaecide.
4) Using chlorine and not your SWCG, you want to raise your Free Chlorine level to 20ppm. Again, you'll just seriously shorten the life of your cell--and they run $400-$600, ball park.
5) "Shock" is a verb, not a noun and when pool stores (like Leslies) use it as one it doesn't tell us much. What's in it is what matters. And Leslies, like many companies, is notorious for NOT saying what's in it: Is it Tri-chlor, Di-Chlor, Cal-Hypo or "Chlorine Free"? So I don't know what it is .
6) That's an awful lot of salt to be adding monthly. Unless you are losing water, salt levels shouldn't change once you hit 3000ppm. Maybe one of our SWCG experts can help.
7) Here's what I think you should do
a) put the SWCG back to normal
b) Add enough chlorine to get your FC to 20. 1 gallon of ultra bleach 8.25% will add about 3ppm of FC...so you need about 5 gallons initially.
c) Check chlorine 2-3x/day and add bleach till you hit 20ppm
d) don't mess with muriatic acid or adding borates now as your pH is fine. It's one of those alligators and draining the swamp things.
e) Brush the pool daily, ESPECIALLY the black algae spots.
f) Vacuum the pool daily, to waste.
g) you should see a change in a few days.

Good Luck!

Re: the extreme addition of salt.

I see three possibilities since he didn't report any obvious errors on the swcg control panel.


1. If the pool has a major leak and he's replacing a large quantity of water every month he may also need to add a lot of salt.

2. When a salt cell gets old and needs replacing it can progressively read less salt than what is in the pool. Get a Taylor K-1766 or at least some aquacheck strips to confirm salt levels.

3. If the salt cell gets a buildup on the sells. This happens if you don't ride herd on your pH levels. At 7.3 it's not likely the problem. That is, unless it was formerly out of control and above 8 or the cell was never cleaned. Get a Taylor K-1766 or at least some aquacheck strips to confirm salt levels.

In conclusion:Get a Taylor K-1766 or at least some aquacheck strips to confirm salt levels. Also, follow the manufacturers procedures to acid wash the salt cell. This will remove any buildup if that is the cause.

Any one of these would result in the SWCG not producing chlorine properly.


3 Gallons of muriatic in that pool is going to take it down to pH 6.6. Yikes.

I would turn the SWCG off completely right now while you are working to clear the pool and just use bleach. Then, once things are cleared up, you can turn it back on.

Get a good kit --- Taylor K2006 or 2006C (better buy). Link is here for it and the ones that kelevmor mentioned in the post above:> http://pool9.net/tk/

(Until you registration is completed, you won't be able to see the rest of the forum while you are logged in. So, copy that link and then paste it into a browser window after you log out.)

You might think that kelemvor's, Watermom's and my advice are contradictory, but they are NOT.

'mom's advice is simple: Fix the water first by manual tried-and-true methods before you attack your SWCG and potential problems.

kelemvor's advice is simple as well: See if you have a leak. THEN seek out whether your SWCG is giving you bad readings. And a confirming test kit for salt levels is something EVERY SWCG owner should have, even if you almost never need to use it.

My advice is on how to clear the pool and what NOT to do (add acid).

So...work on clearing the water and finding the leak. When that's done, address what's going on with your SWCG.

Thanks Carl & Kalemvor,

I will follow your plan towards the end of the week, when I can be around.

1. Shocked with Cal Hypo 73%. Hope I can finally be ahead of this and keep it away.
2. Pool loses about 3-4 inches/week in summer depending upon dew point, and has done consistently. Loses a lot less in winter, even with pump running similar hours.
3. SWCG appears to be fine (clean), reports increased salt after being added, flashes if I put too much in. Chlorine levels appear to be fine unless the SWCG reports needs more salt. I followed builder's suggestion for salt, and only add when SWCG suggest salt levels are reducing.
4. Brushing isn't always easy - often away from home 14 hours/day, and lose light. so that is an area I need to work harder at.
5. Obtaining strips for salt - cynicism isn't pretty, but always good to be sure, thanks for links
6. Muriatic - OK leaving it on the shelf, I know how to take instruction

Cheers

I sent a lengthy reply, which does not appear to have posted, however I short - many thanks, I will employ all of your suggestions.

Pool was shocked with cal-hypo 73%
SWCG appears to be working fine, will switch off whilst using bleach
Water drops 3-4 inches per week in summer, but a lot less in winter - pump running each time, suggests no major leak
Will buy test kit as suggested, thanks for links
Muriatic acid is back on the shelf to gather dust
Will increase brushing as much as possible - loooooong hours at work

Thanks for all the advice

Stephen, when you post it will go into a moderation queue to be approved by one of us before it will appear on the forum. We try and empty out the queue multiple times per day so it usually isn't too long before it appears. A way to avoid the moderation queue is to become a subscriber if you are interested. Subscriber posts also get priority attention when we get really busy.

OK. When you press the "Reply to Thread" button, as I just did, the Quick Reply box opens and there should be row of 9 buttons, including B for bold, I for Italics and U for Underline. Two buttons to the RIGHT of the U is the "Insert Image" button, to the right of the little globe.