How much chlorine do I need to kill algae, given these parameters?

[MrLeadFoot]

I've read information on this site for years, but this is my first post, so please forgive me if I am not providing enough information, or if I sound like an idiot. I am already kicking myself in the rear for making dumb decisions, as you will see below.

I've been battling this dark green (black algae) that clings to the same areas on the pool walls and stairs every year during the warmer weather. Every winter it dies, but as soon as the weather warms up, it comes back, and plagues me all during the warmer seasons, especially in the hot summers here in Sacramento, CA. I always used the cheap OTO test kits, and my water always stays pretty neutral in PH, with chlorine being my biggest "fluctuator". I made the same mistake many pool owners do by thinking I need to float tabs and "shock" with pool shock packets. I also add copper algaecide every year. While this regimen worked for a few years, it gradually became worthless as far as the black algae is concerned, due to what I now know must have been me unknowingly raising my CYA levels the whole time. In fact, last year, I went to two tab floaters, thinking that would be a good way to get more chlorine in the pool!

Well, I finally got myself a good Taylor test kit, and tested everything today. From what I think I've learned on this site, I believe I am good everywhere, except for my CYA levels and Chlorine to CYA ratio, so I am looking for help. Pertinent information, and test results from today are as follows:

26,220 gallons, NSWCG

FC 1.5
CC .5 (not sure if combine chlorine can be lower than free chlorine, but that's what the test showed)
CYA 100 (fwiw, I had to do the diluted test because the regular test wouldn't even register my CYA levels)
PH 7.4
TA 70
CH 340

Now, I understand that the right way to reduce CYA is to replace water, but where I live it will cost me an arm and a leg to do so. For example, my water bill is $100 a mo. already, and that's pretty much only watering enough to keep things alive on my 1/3 acre parcel. I can't imagine how much it would cost to replace half my pool water!

I theorize that one reason why this algae is more under control in the winter is partly due to the fact that we get pretty heavy rains in the winter which helps dilute my pool water, thus lowering my CYA levels. But then, like an idiot, I've been blasting the CYA right back up again by using tabs and shock in the warm weather!

So, I was hoping there might be a way for me to crank up the chlorine level for now to deal with the algae, to get me through the rest of the summer, and let nature take its course this winter by allowing the heavy rains to lower my CYA levels. I, of course, will immediately stop the tabs and shock, but what I want to know if what I am trying to achieve is possible. If so, can anyone tell me how much liquid bleach of chlorine I might need to get my FC level up high enough to kill off the algae?

If it matters, the water in the pool is always crystal clear, never cloudy, and I have never had an algae bloom. the ONLY algae is the black algae on the plaster surfaces I mentioned above.

Thank you so much in advance.

 

[YippeeSkippy]

Welcome to TFP, Leadfoot <lol, driving record??>
I venture to say you do need to drain at least half your water... if not for the CYA than for the copper you've been adding. I wonder if some of what you're seeing might not be copper staining along with algae?
Can you take a picture of it for us?

The cost of water has to be balanced with against the cost of liquid chlorine at higher levels necessary for a SLAM process necessary to clear the pool of algae? SLAM Process
Have you seen this showing how high your FC level would need to be? --> FC/CYA Levels
If you have algae you need to clear that up with lots of liquid chlorine and a good strong brushing daily.

Right now your FC is woefully deficient and just letting the algae run rampant.

You need to decide if you can drain half the water (even if done in smaller but repeated steps) then perform a SLAM process using only liquid chlorine.

Which test kit number did you obtain? Does it have the powder FAS-DPD test for FC and CC?

Maddie

 

[JJ_Tex]

If it is black algae, pool school has a good article on it. Step 1 is to get a wire brush and get ready for lots of brushing. I still remember attacking black algae with it as a kid in my parent's pool.

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

 

[MrLeadFoot]

Welcome to TFP, Leadfoot <lol, driving record??>

I have a clean driving record, likely due to going so fast they can't see me to ticket me.

I venture to say you do need to drain at least half your water... if not for the CYA than for the copper you've been adding. I wonder if some of what you're seeing might not be copper staining along with algae?

I don't see how one could possibly confuse algae with a stain. Regarding the copper, I don't think it's chelated, because no blondes have ever left my pool with green hair, nor do I see staining from it, so I think it precipitates out or something.

The cost of water has to be balanced with against the cost of liquid chlorine at higher levels necessary for a SLAM process necessary to clear the pool of algae? SLAM Process
Have you seen this showing how high your FC level would need to be? --> FC/CYA Levels

Yes, I have. Do I really need to SLAM? I could've sworn I previously read somewhere (on this site) that 7.5% FC of CYA levels is what you need to be at to kill off algae, which in my case would be 7.5, but the chart says my target should be 11-13. Nevertheless, I brushed it yesterday, and today cleaned my filter and brushed it again. This evening I added 4 gallons of bleach (6%), covered it with a solar blanket, and turned on the pump. 90 minutes later I tested it, and I am at 11.5. Do you think this is high enough to kill the algae? I think it's supposed to be, and was planning on leaving the pump on, and checking the level tomorrow morning, and again tomorrow evening so I can ensure I keep the level up.

BTW, what is the effective difference between minimum and target levels?

f you have algae you need to clear that up with lots of liquid chlorine and a good strong brushing daily.

When I brush it, even with a steel brush, the topmost layers break off, but it has a hold in the small pores of the plaster, so it keeps coming back in the same spots. I don't want to grind off the plaster by brushing too hard, you know what I mean?

Right now your FC is woefully deficient and just letting the algae run rampant.

This is exactly why I asked if anyone knew how much chlorine I would need to add to get my FC up high enough to do its job.

You need to decide if you can drain half the water (even if done in smaller but repeated steps) then perform a SLAM process using only liquid chlorine.

I was hoping for an alternative due to cost of water where I live. It's a corrupt county, so they rape us on utilities where I live. Hence my mission to find the right formula to kill the algae, and hold me over until the winter rains this year.

Which test kit number did you obtain? Does it have the powder FAS-DPD test for FC and CC?

K-2006, and it indeed has the FAS-DPD test, which is what I used.

 

[MrLeadFoot]

If it is black algae, pool school has a good article on it. Step 1 is to get a wire brush and get ready for lots of brushing. I still remember attacking black algae with it as a kid in my parent's pool.

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

Brushing is useless when your chlorine level can't kill it. It comes back faster than you can brush, and too much brushing with a wire brush will wear out plaster, so I am trying to find the proper chemotherapy formula that will kill it off. I just re-read the article, and I see it recommends that I get the FC up PAST the higher end of the target range. I missed that when I read it before. I will test again tomorrow and see what I've lost and what I need to add to get there. I'm hoping the solar blanket will help prevent burn off during the day tomorrow.

 

[Flying Tivo]

CYA 100 (fwiw, I had to do the diluted test because the regular test wouldn't even register my CYA levels)

If you did the diluted test and got 100, then your CYA is 200, which is unmanageable for a slam process. It would be obligatory to drain at least 3/4 of your pool volume.

 

[MrLeadFoot]

If you did the diluted test and got 100, then your CYA is 200, which is unmanageable for a slam process. It would be obligatory to drain at least 3/4 of your pool volume.

I got 100 using the diluted test. Sorry if I wasn't clear about that. Wait, that's still not clear. The diluted test gave me a reading of 50, so my net result is 100. That means there's hope without draining, right?

 

[JJ_Tex]

Its really a 2 step process:
1) Brush to remove the waxy protective coating of the black algae so that the chlorine can kill it. You have to do this multiple times a day while keeping your chlorine high
2) Keep your chlorine high enough to kill it, which is between the target and slam amounts. For your CYA of 100 that would be maintaining FC somewhere between 13 and 39 for your "chemotherapy formula".

 

[MrLeadFoot]

Thank you for the clarification. Glad to hear that I only need to remove the top layer. I'm already good at that part.

I know that 4 gallon got me from 1.5 to 11.5, but is that rise linear? What I mean is, my net rise is 10 and I used 4 gallons. If it's a linear thing, then 1 gallon is goodfor a 2.5ppm rise, so 2 more gallons would put me at 16.5. Surely, raising FC can't be that simple, can it? ?

 

[an1vrsy]

What percentage chlorine are you using, 6% bleach from grocery store, 10% from Big Box store or 12.5% from your local pool store? When I plug your pool volume and other numbers into PoolMath using 10% chlorine, you would need 148oz to from the minimum 8ppm to upper target 13ppm. Now if your current chlorine level is lower than 8 ppm then you'll need a lot more LC.

 

[MrLeadFoot]

As I mentioned in a previous post, I used 6% bleach. I bought 10 gallons, and used 4 to get from 1.5 to 11.5. OK, so I just used PoolMath, and it looks like it really is that simple. According to PoolMath about 1 gallon will raise my FC by 2.5ppm. The silver lining with having a high CYA is that I should be able to more easily maintain the higher FC level, because the high CYA will prevent it burn off quickly, right?

 

[an1vrsy]

You'll still probably lose between 2.5 - 4 ppm free chlorine every day. Your high CYA requires high chlorine to keep algae at bay. However, in your case you already have algae so your FC loss will be higher fighting algae and UV.

 

[DuaeGuttae]

You’ve been getting good advice. I just wanted to pop in with a couple of answers that I perhaps missed above.

The difference between minimum and target FC levels is to account for daily loss due to sunshine and bather load. The minimum is just that, the level you don’t want to drop below (and I don’t even want to hit it). The target is a range where you dose your chlorine so that accounting for your daily loss, you always remain above the minimum.

If you have black algae, you aren’t dealing with the normal daily maintenance or target levels. You need extra chlorine in the water to make sure you have enough available to kill that algae faster than it can reproduce. Algae grows much faster in warmer water, which is part of why you have more trouble in the summers.

When we bought our house two years ago, we had algae (not black, though) and a high CYA level. I think it was a little lower, but still about 90. Water is a major issue in our community, and we could not drain. I slammed. It was a lot of chlorine, but it worked.

We collect rainwater as much as possible because our water is so restricted. It is also a benefit to us to use calcium and TA free water because those are so high in the groundwater here. (At this point we’re back to hose water for the pool, because the rainwater and air conditioning condensation go to my garden, especially the calcium-hating blueberries.). If you expect heavy rains in fall or winter, I would start thinking now about how best to take advantage of those. (We added 3 large rain tanks (totaling 1,000 gallons) to the small ones we already owned.)

Draining is easier, of course, which is why it’s so often recommended. There are exceptional cases, though, and you can use the same science to make it through. You just need to know up front that it will take a lot of chlorine and a lot of commitment and a lot of patience.

I hope this gives you some encouragement that you aren’t the only one to have dealt with water problems. I think @Richard320 might have some insight, too.

 

[MrLeadFoot]

Thank you for the reply, understanding my need to think outside the box due to my predicament of outrageously expensive water, as well as your words of encouragement.

This morning, I brushed it again, which was 10 hours after getting the FC up from 1.5 to 11.5. The brushing was much more effective in breaking up and removing the algae from the plaster surface, and what is left on the surface of the plaster is much more faint. It's not gone, by any means, but I can see a BIG difference. From that very noticable difference just from brushing the algae, I think all this time the FC has just been way too low to have ANY effect. I will look closely again at it this evening, and will test the FC level. I am almost tempted to experiment by keeping the FC level in the target range I'm in now, since I'm seeing such an improvement already. I'm wondering if it's possible that the algae was comfortable at 1.5 FC, which is what it's been exposed to all this time, thus is dying at 11.5, which is 10x the original FC level, or if I should just add enough LC to get the FC level up to 16.5. What do you think, is that wishful thinking, and science says that the algae will definitely not die at 11.5 FC?

You’ve been getting good advice. I just wanted to pop in with a couple of answers that I perhaps missed above.

The difference between minimum and target FC levels is to account for daily loss due to sunshine and bather load. The minimum is just that, the level you don’t want to drop below (and I don’t even want to hit it). The target is a range where you dose your chlorine so that accounting for your daily loss, you always remain above the minimum.

If you have black algae, you aren’t dealing with the normal daily maintenance or target levels. You need extra chlorine in the water to make sure you have enough available to kill that algae faster than it can reproduce. Algae grows much faster in warmer water, which is part of why you have more trouble in the summers.

When we bought our house two years ago, we had algae (not black, though) and a high CYA level. I think it was a little lower, but still about 90. Water is a major issue in our community, and we could not drain. I slammed. It was a lot of chlorine, but it worked.

We collect rainwater as much as possible because our water is so restricted. It is also a benefit to us to use calcium and TA free water because those are so high in the groundwater here. (At this point we’re back to hose water for the pool, because the rainwater and air conditioning condensation go to my garden, especially the calcium-hating blueberries.). If you expect heavy rains in fall or winter, I would start thinking now about how best to take advantage of those. (We added 3 large rain tanks (totaling 1,000 gallons) to the small ones we already owned.)

Draining is easier, of course, which is why it’s so often recommended. There are exceptional cases, though, and you can use the same science to make it through. You just need to know up front that it will take a lot of chlorine and a lot of commitment and a lot of patience.

I hope this gives you some encouragement that you aren’t the only one to have dealt with water problems. I think @Richard320 might have some insight, too.

 

[bmoreswim]

Thank you for the reply, understanding my need to think outside the box due to my predicament of outrageously expensive water, as well as your words of encouragement.

This morning, I brushed it again, which was 10 hours after getting the FC up from 1.5 to 11.5. The brushing was much more effective in breaking up and removing the algae from the plaster surface, and what is left on the surface of the plaster is much more faint. It's not gone, by any means, but I can see a BIG difference. From that very noticable difference just from brushing the algae, I think all this time the FC has just been way too low to have ANY effect. I will look closely again at it this evening, and will test the FC level. I am almost tempted to experiment by keeping the FC level in the target range I'm in now, since I'm seeing such an improvement already. I'm wondering if it's possible that the algae was comfortable at 1.5 FC, which is what it's been exposed to all this time, thus is dying at 11.5, which is 10x the original FC level, or if I should just add enough LC to get the FC level up to 16.5. What do you think, is that wishful thinking, and science says that the algae will definitely not die at 11.5 FC?

You are setting yourself up for failure by being tempted to experiment. We espouse processes not experiments. A SLAM is the proper way to eliminate algae and move forward successfully. Anything less will put you back where you started. Your pool may clear and algae appear gone, but the slightest hiccup, or possibly even nothing, you will see green on your walls or slightly cloudy water.

You need to win, not tie, with algae. Tying with algae is losing.

 

[MrLeadFoot]

OK, no experimenting. Thanks for bringing me back down to earth! I just got excited to see such a change simply from getting my FC up. I will go home this afternoon, check levels, then brush again and add LC to get my FC levels up. FWIW, interestingly, I've never had cloudy water from an algae bloom in this pool in over 20 years. Just the cyanobacteria (black algae) I am dealing with now.

 

[Flying Tivo]

Just the cyanobacteria (black algae) I am dealing with now.

Algae all the same!

 

[MrLeadFoot]

OK, I got home and checked my FC, and it was 9, so it only dropped 2.5 in 24 hours. I don't think that's too bad, or is it? I looked closely at the algae, and the remnants that are "dug in" on the walls and stairs are much reduced yet again! When I brushed over the spots again, as has been recommended, all around the remnant spots I kicked up a very light grey dust, which looks to me like dead algae. Regardless of what it is, even though it's been recommended that I run much higher numbers, it's clear that this process is working, and much quicker than I thought, too! So as not to experiment, I added 2 gallons which will bring me up to 14, according to PoolMath, and what I have experienced thus far. I know I'm not out of the woods yet, but thank you all so much for your time and advice up to this point, because things are going quite swimmingly!

Now, does anyone how much a pool of my size with "normal" CYA levels might drop in FC over 24 hours during the peak of summer? Thanks again.

 

[frogabog]

On a normal day any pool will lose roughly ~50% of the FC. Normal CYA levels bring that somewhere around 2-4ppm for most pools, regardless of size.

You've been given valid and good advice above. It is your choice whether to follow it or not, but the chances of full success are slim to none unless you follow the SLAM Process exactly. Losing 2.5ppm FC when you can see algae means your chlorine isn't working very hard at all, and once it can't work anymore due to your high CYA level... it's not working at all. Probably why it's not disappearing rapidly. When chlorine is battling organics, it's rapidly consumed and needs to be replaced to continue it's battle. Is there no way you can drain and refill 50% of your water?

Lots of people have seen some progress like you're describing with other methods to clear algae, but it almost always comes back. Then they come here and learn how to do it so that it doesn't come back.

Dead algae is white, and it will revive itself even if white if FC levels aren't maintained at SLAM level. This has happened to thousands of pools attempting to experiment. TFP will be here when you need further assistance.

 

[MrLeadFoot]

Please understand that I am hearing and do comprehend the standard procedures that have been presented to me thus far. But, right now I simply can NOT drain and refill 13000 gallons. That's my dilemma. In lieu of that, what i am trying to do is do what I can within my limits to deal with the algae for now, until winter when I plan on using water from our heavy winter rains to dilute my pool (partial drains before each storm).

This said, I may have misunderstood parts of your post, but you said if the algae isn't disappearing rapidly, it's not working, yet after only 24 hours, I only see faint remnants of where it's dug into pores in the plaster on the walls and stairs, whereas just yesterday morning there were larger thick dark green slimy patches. Isn't that pretty quick progress? I will check again tomorrow morning and evening to ensure it's still clearing up, and I was thinking that if it continues to clear up, then whatever I'm doing must be working. I did raise my FC to above the upper end of my target range regardless of the progress I'm experiencing right now, and plan to go even higher tomorrow when I get more LC. Of course, if progress slows, then I will need to take a different course of action.

FWIW, prior to me testing with a real kit, and finally getting my FC up to 11.5 yesterday, I was running what I now know was 1.5 FC, for years. The algae would grow and I would brush it, and whatever did not come off with the brush would start to grow back very quickly, so quickly that I could see it starting to come back as soon as the very next day. Conversely, what I have experienced in the last 24 hours is something that has never happened before. I brushed it off yesterday, and instead of what couldn't be brushed staying on the plaster, this afternoon there's even less of what was left after my brushing yesterday. It's not that it just didn't start growing back right away; without any brushing for 24 hours, it actually died back even further. I'd say roughly 50% of the remnants that remained after yesterday's initial brushing are gone. In fact, when I told my son this afternoon that I needed to brush it again per the instructions of this forum, and get the FC levels even higher than the Target level defined by Pool Math, he said, "But, the places where the algae was looks pretty darned clean already."

How much faster would I see this algae retreat, if I was doing it correctly?