Pentair 5G pool lights help. What is this?


Bronze Supporter
Aug 11, 2016
Hudsonville, MI
Hey Group. Long story short. I saw something that looked like a shadow on the underside of my lights in the pool wall. Under closer inspection, I believe it is rust. I had the pool installed in September of last year. I removed the light from the niche and this is what I found. What would this be coming from the hole in the back?







Bronze Supporter
Aug 30, 2016
Pittsburgh PA
Looks like dirt that got into the PVC conduit that the line runs through. It's just now working it's way down hill to the light niche.

Sure hope it's not rust! I just installed the same light in my salt pool.


Gold Supporter
Sep 8, 2016
Is the conduit PVC? Id guess it is. If yes, there is little chance it is rust. The dirt explanation seems like a good one. does it scrub off?


Well-known member
Apr 5, 2017
My first impression is mud. Can you "scoop" it with net. you should be able to tell by touch.
Being from the south we have that red clay, Ultisol, which is what I first thought in the pool floor and niche pics.

Using your profile location, it looks like your region has alfisols. Has iron.

My initial guess is maybe it's rust from the soil. Perhaps decoupled conduit allowed it into the niche where it rusted in the niche.

You know your area better than I, check the map:
soils <-- of Michigan

Gig'em Aggies.

edit: I used the bottom two maps to get soil region. Last shows general of "A2". One above it was also relied on to get most probable soil type. if you don't know for certain your soil type call you local ag extension office.
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Bronze Supporter
Aug 11, 2016
Hudsonville, MI
I just got off the phone with Pentair (again) and the local service company states that some of the rust is coming from the bronze screw that is used to hold the light into the niche. Also, that my electrical installer should have sealed my conduit with potting compound. I'm so confused. I went back and looked at Pentair's install manual and it states to only use the special bronze screw. See image below.
5G.Installation and Users Guide.jpg
Secondly, where does it say anywhere that the niche needs to be sealed to the pvc conduit?

Any info to help me when I contact my electrician would be greatly appreciated.

I'm sick.


Bronze Supporter
Aug 11, 2016
Hudsonville, MI
They come back with "water chemistry....bla bla bla" I'm in contact with the electrician installer and seeing what he used to connect the pvc conduit to the niches. It's going to be a battle I'm afraid.


Well-known member
Mar 10, 2017
House Springs
"Rust is iron oxide, formed when iron reacts with moisture and oxygen from it's environment. Bronze contains no iron, it is an alloy of copper and tin (and a few other metals such as zinc, but these are usually minor additions, the major constituents do not vary) so cannot form rust."


In The Industry
Jul 8, 2010
Ashford, CT
When I first saw it I thought it was Galvanic Corrosion - resulting from a light electrical current being in touch with the metal.

That would be a lot of rust.. in fact a massive amount of rust for a year or two.

IF it is rust I would see if the light is wired and grounded properly at the J box-- but then read this article.

Mystery Stains in Salt Generator Pools - AQUA Magazine

The solution would be to install a sacrificial anode (a softer metal like zinc) that absorbs this charge vs your light niche. Also replace all the niche screws with stainless steel.

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