Clear and blue pool turns green after adding chlorine and muriatic acid

Motor

LifeTime Supporter
Aug 12, 2013
16
I have searched for this and not found anything definitive. If anyone has information as to why my pool turns green for a couple days after I add chlorine liquid and muriatic acid, please help I’m curious what’s going on. There is some organic matter in the pool from dirt blowing in and some leaves that have sunk to the bottom a few days ago but nothing excessive.

I heard from someone that it’s because I’m waiting too long in between adding chlorine. And that the chlorine is dropping to zero, and then when it spikes up the water turns green but I don’t understand why. Any help or answers would be greatly appreciated! Thanks
 

mknauss

Mod Squad
TFP Expert
Bronze Supporter
May 3, 2014
23,001
Laughlin, NV
Is it green or yellow? Iron in your fill water? Do you have a test of the fill water as well as a complete set of test results from your pool water?

Where is this pool located? Please add your Location to your Settings. Also a signature would be great - see Pool School - Getting Started

I do not think it is from organics in the pool being oxidized by the chlorine. Letting your FC go to zero is not good, but that is up to you.

Take care.
 

Poolboy22

New member
Nov 8, 2017
1
Jacksonville Florida
I have searched for this and not found anything definitive. If anyone has information as to why my pool turns green for a couple days after I add chlorine liquid and muriatic acid, please help I’m curious what’s going on. There is some organic matter in the pool from dirt blowing in and some leaves that have sunk to the bottom a few days ago but nothing excessive.

I heard from someone that it’s because I’m waiting too long in between adding chlorine. And that the chlorine is dropping to zero, and then when it spikes up the water turns green but I don’t understand why. Any help or answers would be greatly appreciated! Thanks
A big cause of a green pool is a low chlorine level. If you let your pool sit at a low/none chlorine level it would be a good reason why the pool keeps turning green. Don't let it drop to 0.
Is this a recurring problem? If it is I would make sure when you do treat the algae, you eventually kill it all off and not just some.
 

Donldson

TFP Expert
LifeTime Supporter
In The Industry
Jun 12, 2009
3,958
NW Ohio
I do not think it is from organics in the pool being oxidized by the chlorine. Letting your FC go to zero is not good, but that is up to you.
Agreed, a color change immediately after adding a chemical usually indicates metals. Algae would be forming and showing itself more consistently than what you are describing. Is the water cloudy green or more clear green?

(Not that allowing your FC to drop to zero is a good thing, it will cause problems and you shouldn't allow it to, but I don't think this is the cause of the issue you are describing)
 

duraleigh

Admin
Mod Squad
TFP Expert
Platinum Supporter
LifeTime Supporter
In The Industry
Apr 1, 2007
32,864
Sebring, Florida
That is caused by iron in your pool water. The addition of chlorine raises the pH long enough for the iron to precipitate into a visible solid particulate. The pH slowly returns to normal over a couple of days and the iron returns back to a soluble state. Chances are very good you are filling from a well.

Dealing with iron is troublesome but it can be managed. Start by having your water tested for iron and confirm the results. You will need to add a sequestrant to hold the iron in solution or stop using the source water you are currently using.
 

Motor

LifeTime Supporter
Aug 12, 2013
16
I’m in Los Angeles.... so no well Water. I have old copper pipes from filter to pool. In ground, 30k gallons.

It’s not algae I don’t think because water is clear and blue and when I test, at end of week or so PH is usually a little high but not crazy high. It’s strange because water within an hour of adding chemicals turns green, slightly cloudy. Then after 3 days, returna ti clear blue. Think it could be Cooper in the water?
 

Swampwoman

TFP Expert
LifeTime Supporter
Apr 27, 2012
3,834
Grand Rapids, MI
Yes, Motor, it is quite possibly trace copper, but it's also possible your municipal water supply has trace iron as well or that something in your pool has corroded and contributed metals. With metals, a concentration greater than .3 ppm can stain. You are likely below that since the only time you're seeing anything is when you add chlorine (oxidizing).

in either case, you could add a HEDP-based sequestrant to reduce its visibility in higher ph and reduce possibility of staining - eg Metal Magic. You can also deliberately keep your ph lower, eg 7.2-7.4ish, to prevent the discoloration of the water.

Since metal concentrations tend to increase over time due to evaporation and continued additions if in source water (or additional leeching in the case of pipes or corrosion,) you may eventually need to look into the source, and once identified, take measures to reduce or dilute. Eg. replace those old copper pipes...But if you have no other "symptoms" right now, you can wait and see.

To manage metals well, it's first necessary to manage your chemistry well through testing frequently and establishing a good sanitization routine. To that end, TFP is your friend. Be sure to use a recommended test kit (http://www.tfteskits.net ) , understand the [fc/cya][/FC/cya] ratio and undertake the maintenance philosophy described in our Pool School ;)
 

Motor

LifeTime Supporter
Aug 12, 2013
16
Okay... I have the full TF Test kit and don’t think
It has a copper test? I’ll take a closer look. . And I’m almost 100% sure it’s not iron... I’m going to take a sample over to Leslies pool to test for copper a few times and see what comes up. It took about a week for the green to go away and the clear blue to come back. Checked PH and it’s now low, so I added 4 more gallons of chlorine and water is staying blue and clear. I think the muriatic acid def caused the reaction to occur.

Also, no copper Algecide has ever been used in this pool. So only metal could be coming from old 50 year old copper pipes. I’ve heard they can be sleeved, but that it’s better to remove and replace them. But how in the world do you remove and replace copper pipes from the main drain?! Dig a huge trench next to the pool?

I’ll report back results of the test for metals.

Thanks!
 

mknauss

Mod Squad
TFP Expert
Bronze Supporter
May 3, 2014
23,001
Laughlin, NV
TF100 does NOT include any metal tests.

Pool store should be able to do it. Just be wary of any potions they try to sell.

It is very possible that the copper pipes have added copper to your water. Low pH accelerates that process. Have you every used Trichlor (aka pucks) in the pool? They are very acidic and can drive pH very low and TA towards zero unless monitored.

Take care.