beautiful pool turned dark green

[danielsonway]

Greetings,

I am a new owner of a beautiful pool in Arizona for about a year. The first year I had somebody take care of the pool. Then I took over. Just adding chlorine tables, weekly shocks and backwash. Things looked okay until I took a month long vacation. When I was back I found the pool green with algae. I tried brushing, shocking, and backwashing frequently to no avail.

Searching on the internet, found Trouble Free Pools and immediately ordered my TF-Pro kit. It just arrived. Please see attached my test results.

There is no chlorine left. PH is very high. CYA seems to be at 90. TA is undetermined because after adding 10 drops I saw hardly any change in color from green to red.
A couple of days ago, I did add 1 gallon of 14.5% muriatic acid. Not sure what effect it had.

Please advise. Many thanks in advance.

 

[DrewLG]

Welcome. That photo is great.

If you've read through some of the Pool School articles or the wiki, you'll know that your high CYA is due to the tablets and possibly also the shock, and you'll also know that the TFP maintenance method is pretty different from what a pool service typically does or what a pool store typically recommends.

The method here starts with buying a good test kit, which you've already done, and then eliminating all algae with what we call a SLAM (Shock Level And Maintain): using liquid chlorine to raise the pools free chlorine concentration to 40% of your pool's CYA concentration, and continuously maintaining that level while brushing the walls and cleaning the filter until the algae is gone (i.e., until free chlorine is no longer being lost to algae). SLAM info is in the Pool School articles and wiki, and people here will be more than happy to give advice if you have any questions or concerns.

With your high CYA, a SLAM will require a lot of liquid chlorine -- tens of gallons -- because you'll need around 4 gallons of 12.5% chlorine just to get to the necessary 36ppm FC level, and then you'll need to maintain that level by testing the water and adding more chlorine multiple times per day until the algae clears. Which could take a week or two, or more.

It would be faster and cheaper to first lower the CYA concentration by doing a partial drain and refill, if you can. There's an article on draining in the wiki.

Anyway, after the algae is gone, the TFP method is to maintain FC at around 10% of CYA concentration to ensure that there's always enough hypochlorous acid (HOCl, the chlorine compound that does all the disinfecting) in the pool to keep the water sanitized and algae-free. That FC maintenance can be performed with either liquid chlorine or a salt-water chlorine generator, but not with tablets or powdered shock -- because the solid forms of chlorine contain either CYA or calcium, both of which are undesirable at high levels, and both of which will accumulate and remain in the pool water more-or-less forever, or until the water is drained.

 

[Britali]

Looks like you used a 25ml sample for the TA…use the 10ml sample test. Also muriatic acid (MA) will lower pH and TA. If your pH is still high you can add more MA but make sure you do not add enough to drop below the 7’s. BUT if you are in SLAM for the algae, anything above 10pm for FC will make pH tests unreliable.

The advice Drew gave is great, especially concerning your CYA & SLAM. You will want to lower your CYA if you do not want to have to use tons of chlorine.

 

[mknauss]

Welcome to the forum.

First, do the CH (calcium hardness) test. If you are not using soft water for fill water, it is likely you have very high CH.

Then you can determine how much water to exchange. With a fiberglass pool you likely can drain with out issue, but an exchange is safer in regards to your pool stability. See Draining - Further Reading

 

[danielsonway]

Thank you DrewLG, Britali, and mknauss for your detailed replies.

I actually have an SWG. When I bought the home, my pool guy preferred to use tablets and just ignored the SWG. Since I started maintaining (trying to, that is) my pool, I decided to switch from tablets to SWG and added 3 bags of salt about a month ago into the pool. I did not see any noticeable increase in chlorine levels though. I need to learn more about how SWGs work and how best to maintain them.

So I have two questions. 1. How do you factor in the above info? Do I need to do anything different at this point? 2. I have many bags of powdered shock left over. Can I use them now to get rid of the algae and then do water exchange to reduce CYA?

mknauss: my strip test showed my water hardness is high. I'll do proper testing before I start the water exchange. Thanks for the tip.

 

[DrewLG]

I actually have an SWG.

Good, that will make chlorine maintenance easy once you've eliminated the algae from your pool.

When I bought the home, my pool guy preferred to use tablets and just ignored the SWG.

You did great by firing him.

I decided to switch from tablets to SWG and added 3 bags of salt about a month ago into the pool. I did not see any noticeable increase in chlorine levels though.

Once there is enough salt in the water for the SWG to work (around 3000-3500ppm), there is no need to add more unless water has splashed or been drained out of the pool. The SWG produces chlorine gas from the salt, the chlorine gas reacts with the water to form HOCl to disinfect the pool, then the HOCl eventually degrades back into salt and the cycle repeats.

The SWG runs (at an output percentage that you can select, from 0% to 100%) whenever water is flowing through it at a rate above some low threshold. You don't get more chlorine gas by adding salt or by increasing the pump's flow rate; you only get more chlorine by increasing the output percentage or increasing the pump runtime.

So I have two questions. 1. How do you factor in the above info? Do I need to do anything different at this point?

An SWG is good for maintaining the free chlorine level in an algae-free pool, but it can't produce enough chlorine gas to suddenly raise FC to a high level. So the presence of the SWG doesn't really change your plan.

You still need to do a SLAM to eliminate your algae, and you'll still need to use liquid chlorine to get enough FC for the SLAM. The SWG's slow-but-steady contribution to FC would be basically irrelevant; you should probably turn it off until the SLAM is complete.

2. I have many bags of powdered shock left over. Can I use them now to get rid of the algae and then do water exchange to reduce CYA?

Probably not.

If the shock is Trichlor or Dichlor, it's a definite no. The large amounts of CYA you'll be adding will make your FC requirement skyrocket, which will require even more shock which will add even more CYA, etc. Even if you could complete a SLAM that way, you'd end up needing to perform a 90%+ water exchange to get CYA to a reasonable level afterward. Plus, those are both WAY too acidic to safely use in the quantities you'd need.

If the shock is Cal-Hypo, you could maybe do a SLAM with it. You'd be adding a damaging amount of calcium that you'd need to drain after, but you're already planning to drain for CYA anyway. The big problem is that you'd need a LOT of it. How many bags do you even have?

Really, it would be best to exchange water until the CYA gets down to at least 60, with lower even better, and then do the SLAM with liquid chlorine. Sell the powdered shock on Craigslist.

 

[Britali]

I would think you would want to drain & replace the water like Drew suggested to bring down your CYA from 90 to 60 BEFORE you SLAM so it is much easier to maintain SLAM levels to get rid of the algae after CYA lower. For example, on my pool I would have to maintain FC 35 at CYA 90 vs FC 24 at CYA 60. You can plug the different CYA levels in Pool Math app to see your differences. You will have to replace about 30% of your water to get to CYA 60 but definitely test along the way to see where you are.

After you get CYA down, then check pH make sure in 7.2 -7.5 range because cannot get reliable pH readings with FC over 10 when you do SLAM.

Once all that is situated, you can start SLAM. Maintain your FC SLAM level (can check every couple hours at start), brush couple times days daily, vacuum, & backwash when needed until SLAM complete.

SLAM - Shock Level and Maintain

We’ve all had to deal with a green pool. Clear algae from your pool with a SLAM! Read here to use shock level and maintain to clear your pool.

www.troublefreepool.com

 

[Britali]

And best to use liquid chlorine so no hidden extra issues you do not want

 

[danielsonway]

I just placed an order for a pump to exchange water in my pool. I decided to follow the TFP advice and use liquid chlorine after reducing CYA.

I have one more question in terms of timing. I may be traveling for a week soon. Do you recommend to start the SLAM process before I leave or after I am back? If before what is the best way to prepare the pool for a week absence? If after, how do I prevent the problem getting worse until I return?

 

[DrewLG]

I may be traveling for a week soon. Do you recommend to start the SLAM process before I leave or after I am back?

The "M" in SLAM stands for "maintain". The algae in the pool will use up your FC very rapidly, especially at first. You need to be present so you can test frequently (like multiple times per day) and add liquid chlorine to maintain the FC at 40% of CYA concentration. So you can't start and then leave for a week.

If after, how do I prevent the problem getting worse until I return?

I'm not sure I'd even try. If you poured a bunch of liquid chlorine into the pool now, you'd kill a bunch of algae, but under the right conditions algae populations double every 6 hours or so. Which means that as soon as your one-shot chlorine infusion is used up, the algae will come back, and by the time you return there'll be as much as when you left.

I think the other things you might try wouldn't be much better. For example, you could throw some pucks in a floater or two, and keep the pump running to try to distribute the chlorine and filter out dead algae, but even if you did manage to keep the algae population down, that would mean potentially clogging your filter while you're away. Using algaecide, same thing -- plus the other problems (metal staining, etc.) that can come from algaecide use.

Someone else might have a different take, though.

 

[Britali]

How soon is soon? If within a couple weeks, I suggest wait like Drew suggested. If it is a couple weeks out you may be able to SLAM but there may not be a good way to maintain FC (SWG would be able to if you had it dialed into sweet spot) while away for a week to keep the algae away & have to SLAM again when back. Some use pucks while away but they can raise your CYA…by how much in a week I do not know. One of the experts here can advise.

It may be in your best interest to wait unless your trip like a month out and you would like to enjoy it some before trip. But have something in mind for when away or SLAM again on return. SLAM is definitely something you want to do while home (checking FC SLAM levels throughout day, brushing twice a day, vacuuming, backwashing/cleaning cartridges).

 

[danielsonway]

OK, I am back from my vacation. Last night I ran the submersible utility pump for 11 hrs and replaced a good amount of water in my pool.



Now CYA is way down at 30. Yay! But the other measures are about the same as before (obviously I have not started SLAM yet).
There is calcium. It turned pink but after adding 20 drops of R-0012 it did not turn blue.

 

[Britali]

It is hard for me tell what your results are from the picture hehe. Totally cannot tell what your FC is and from what I see in your pic the pH looks higher than 8.2. Could you actually type out the results? Congrats on bringing your CYA down!

I am guessing you still need to SLAM. If pH is 8 or higher, use pool math app to calculate how much MA you need to bring it down to 7.2-7.5 range before you start the SLAM process.

I am not sure if you need to bring CH down or not…the experts can chime in…but the only way to lower that is the same as lowering CYA, replacing water. Not sure if you need to do that but if you do, you will have to raise CYA because it will bring that down too. If, I am remembering right from what I have read, low CH would be an issue in fiberglass pools. I plugged fiberglass & SWG into Ideal levels for pool type and this is what it shows for Calcium.

 

[duraleigh]

danielsonway,

Keep your info under one thread. Responders will seldom see both.

 

[danielsonway]

OK, sure. Is that the practice?
I thought they were somewhat different topics that is why I created two threads.

 

[danielsonway]

I added 3/4 gallon of MA and 2 gallons of bleach. Testing half an hour later, I see no difference.

Britali - sorry about missing numerical results but that is because they are off the charts. The Cl color is lighter yellow than the lowest level, and the ph color is darker pink than the highest level. In other words, my Cl < 0.5 and ph > 8.2 as you mentioned. After adding MA and bleach I still get the same colors. What am I doing wrong? Add more MA and bleach?

 

[Britali]

Do you have the FAS-DPD test in your test kit? That will give you more accurate results. You can test on a 10ml pool water sample & add one heaping scoop of agent instead of 25ml & 2 scoops…then multiply drops by 0.5 (which is the same as divide by 2). That will give you more accurate results on your FC.

As far as pH you cannot dilute it but you can perform the Acid demand test to see how much you need to bring it down under 8.

Are Dilutions Necessary When Testing

 

[duraleigh]

You information is hard to follow. Your first step towards restoring your pool is to post a complete set of test results. While you are waiting for responses, Please read "Pool Care Basics" up in Pool School. We can help get your pool to crystal clear but we need to eliminate the guess work.

 

[danielsonway]

My test results this morning:

FC = 1
CC = 1
TA = 60
CYA = 30
Cl < 0.5
pH > 8.2

I added 3/4 gallon MA and 2 gallons bleach yesterday evening and run the pump overnight.

 

[duraleigh]

You are almost ready to SLAM your pool. A cc of 1 indicates you have organics in your pool so let's get rid of them.

1. Read the SLAM article in Pool School. It should be followed precisely.

2. Using muriatic acid, lower you pH down around 7.2
3. Begin the SLAM by bringing your FC up around 12-14 ppm.
4. Test the FC and CC during your SLAM by adding enough FC to get it back around 12-14.......probably not less than three times daily. This may take 24-48 hours or sometimes even longer.......just focus on keeping your chlorine up to the SLAM level.
5. When your CC tests results in .5 or .00, You are almost done.
6. Perform the OCLT and if your overnight loss is 1.0 FC(or less) you are finished!