Found a source of metal staining in our pool – may be helpful to others!

[Mandy]

Hello everyone, I just wanted to share this with you all.

I have had ongoing issues with metal staining in our pool. Following my last stain removal treatment in May 2017 I have been using an HEDP sequestrant, first as an initial dose, then 250ml per fortnight. However as brown rusty stains are still re-appearing (see photo) – I concluded either I’m not using a sufficient amount of sequestrant often enough or perhaps there’s an unknown source of metal being introduced to the pool.



We are on town water and when I had the tap water tested at the local pool shop in May 2017 it showed iron @ 0.3ppm and copper @ 0.8ppm. Pool water test on same day showed iron @ 0.2ppm and copper @ 0.1ppm. My last pool water test from the pool shop was August 2017 and the levels were iron 0.1ppm and copper 0ppm. Up until I began doing my own testing in July 2017 (thanks to TFP) these levels always hovered between 0.1-0.3ppm for iron and 0-0.1ppm for copper.

We have no handrails or anything metal in the pool apart from the screws on the light which show no signs of rust. I removed the pot plants from the pool yard thinking the water that drains from the bottom may be going into the pool - unlikely but very heavy rain may have made it possible at times.

I then bought some thick white socks and attached 5 socks over the end of the hose prior to topping up the pool (with hose placed into skimmer with the pump running) so that any water introduced goes through the filter before entering the pool. The first time I did this I was very surprised to find all 5 had a brown tinge to them! See photos before and after use. Each time I top up I use the socks and over time they have become very stained.



It turned out the​ tap fittings of my top-up water were to blame. I had a galvanised fitting along with brass taps and it seems these two metals don’t “play” well together. I had a plumber change all fittings to brass (including new taps) and it was amazing to see the amount of rust and crud build-up within them. Following the changeover of fittings I ran a lot of water through the hose onto the lawn to aid in cleaning out the line.



I have since topped up, using new socks over the end of the hose, and the staining is greatly reduced. I may not have solved the problem entirely but believe I have certainly reduced my staining potential.

I intend to have a pool store check my source water again – it will be interesting to see if there is a significant change in the metal levels.

I have had numerous compliments/comments about how beautiful and sparkly my pool water looks and I tell everyone about you and how helpful you have been to me.



I will do another post in the future outlining what I have learnt since joining you which may be useful to newcomers. Thank you for this wonderful resource.

My current test results:-
FC 8
CC 0
pH 7.5
TA 60
CH 290
CYA 80
Salt 4600
Pool Temp 26.5°C
CSI -0.66

 

[kimkats]

Well look at that what a find! I can't wait to see/hear how it goes! Good job with the socks!

Kim

 

[santacruzpool]

Interesting - and a good find.

I wonder if we will have similar problems in the future? I am now worried a bit!

Our pool fill line is a connection off of the landscape irrigation side of our city water supply. At the street side, near the water meter, we have a back flow prevention valve that is required by code for any landscape system. The way this was built is using PVC from the main valve under ground that goes over to just below the back flow setup. Then there are risers from the PVC under gound made from galvanized pipe, elbows, and unions. Each side of the valve is built this way. The galvanized pipe is taped up with a PVC tape where it enters the ground to "prevent" corrosion. Prevent is the big word here. Laser summer, after just 5 years of use, one section of the galv pipe had a pin hole leak in it right at the ground level. When I took it apart to replace the piece of pipe there was a huge amount of corrosion inside the pipe...not sure why so much after only a few years of use.

I am now thinking I should re-pipe this at some point in the future with hard copper pipe...

 

[JoyfulNoise]

This is a common plumbing mistake that's either made when an unknowledgeable homeowner tries to make a DIY repair OR when a plumber/plumber's assistant cuts corners. Galvanized pipe should never be placed in contact with brass or copper fittings as it causes the galvanic corrosion you're seeing. The brass is more noble than the zinc coated steel pipe and so the iron will corrode sacrificially. I had something very similar happen recently where my outdoor spigot sprung a small leak. It was the spigot that the pool plumber had hooked the pool's autofill line to and his assistant (aka, kid barely the legal working age) put a 3" galvanized threaded nipple between two brass unions. Sure enough, 4 years later and the galvanized threads had rotted completely through. It was a cheap, $5 corner to cut but you would have never known about it until the leak happens.

Good find and thanks for posting that!

PS - If, for some unknown reason, galvanized pipe must be used in contact with brass or copper, there is a special type of fitting (union) called a dielectric union. It essentially has a double o-ring seal that electrically isolates the two metals so corrosion can not occur. It's an expensive solution to a problem that can simply be resolved by not putting dissimilar metals in contact but it does exist...

 

[Mandy]

This is a common plumbing mistake that's either made when an unknowledgeable homeowner tries to make a DIY repair OR when a plumber/plumber's assistant cuts corners. Galvanized pipe should never be placed in contact with brass or copper fittings as it causes the galvanic corrosion you're seeing. The brass is more noble than the zinc coated steel pipe and so the iron will corrode sacrificially. I had something very similar happen recently where my outdoor spigot sprung a small leak. It was the spigot that the pool plumber had hooked the pool's autofill line to and his assistant (aka, kid barely the legal working age) put a 3" galvanized threaded nipple between two brass unions. Sure enough, 4 years later and the galvanized threads had rotted completely through. It was a cheap, $5 corner to cut but you would have never known about it until the leak happens.

Good find and thanks for posting that!

PS - If, for some unknown reason, galvanized pipe must be used in contact with brass or copper, there is a special type of fitting (union) called a dielectric union. It essentially has a double o-ring seal that electrically isolates the two metals so corrosion can not occur. It's an expensive solution to a problem that can simply be resolved by not putting dissimilar metals in contact but it does exist...

Thank you for your responses and thanks Matt for that explanation, makes a lot of sense.

Just to follow-up on my earlier post I had both my tap water and pool water checked today at the pool shop. My tap water now reads iron @ 0ppm (down from 0.3ppm) and copper @ 0.2ppm (down from 0.8ppm) so if I can trust these results that looks like a win to me! My pool water tested iron @ 0.1ppm (no change) and copper @ 0.1ppm (up from 0ppm).

Here’s a comparison of my test results vs pool shop test results:-

	My Test	Pool Shop Test
FC	8.5	6.66
CC	0	0
pH	7.6	7.8
TA	60	63
CH	290	189
CYA	80	66
Salt	4600	4200
Phosphates		OVR 5093ppb

I cannot believe the handwritten recommendation from the young guy who did the tests – he advised me to add 1 litre (1000mls) of acid to reduce my pH and when I plug that into Pool Math Effects of Adding Chemicals that would take my pH from 7.6 to 6.46 and my TA from 60 to 41! That is just plain wrong.......... I know better now but for so long I blindly followed their recommendations and was forever adding chemicals, raising this and lowering that trying to balance my water. In hindsight it was never going to happen. I pity those who have not yet found TFP!

 

[Swampwoman]

Thanks for posting your awesome detective work, Mandy. We may have to invent the Mandy Sock Test protocol for metal origin detection