Galvanic Corrosion

[cowman]

This is my first pool. The pool is now 5 years old. I have loved the pool and thought all maintenance and nightmare pool problem stories I have heard were just that, stories. Our pool has always seemed clean and I invested in a TF100 test kit to make sure water was right. Periodically my pool contractor came back to repair what I assume are normal wear and tear. Now I have several problems and I am looking for advice, past experience and maybe just someone to tell me that that is just the way it is when you own a pool.
First problem- One of the ropes to my automatic pool cover broke and we pulled it out to fix it when I noticed some major corrosion around the drum that pool cover is rolled onto. Upon removal even the pool cover was rotting away on the one end closest to the pool cover motor. The drum has been eaten through entirely. Called my contractor and he came and helped and he could not believe that much wear in only 5 years. Of course he figured out that it must have been me not keeping chemicals in pool water correct that caused it! And of course the warranty on the pool cover is not really a warranty just a prorated deal that makes it cheaper to buy a new cover with a new 5 year warranty. Long story short I have a new drum and a new cover.
While here my pool contractor helped change the bulbs in one of my Jandy pool lights. I have 2 lights one on side and one at the end where pool cover is. We changed bulbs on side light. When contractor replaced light he failed to replace seal around light chord and my pool drained down to light in 3 days. That is when I noticed that my pool light at the end of pool is also corroded very similar to the drum.
I have since scoured the internet and have been reading about salt water and galvanic corrosion. I am looking for help from someone who may understand and give me advice on how to prevent this from happening again in the next 5 year and why only one light is corroding and other is perfectly fine. Also can I clean the corroded light or do I have to replace?
Please Help.

 

[loop_pea]

Salt and non-salt water can be corrosive if they are out of balance, but the salt content could accelerate the problem in out of balance water.

Have you seen: http://www.troublefreepool.com/pool-school/water_balance_saltwater_generator ?

Are you familiar with Langelier and Calcium Saturation Index? http://poolcalculator.com can work out the second of these - if the number is very negative, then you will need to do something about it.

 

[Melt In The Sun]

Cowman, how 'bout some photos?

Welcome to TFP!

 

[JasonLion]

If there is aluminum touching the water in the cover system (quite likely) you would benefit from installing a sacrificial zinc anode.

 

[5*pooloperator]

I did a saline retrofit on three existing bodies of water. The salt content of the water brought to light some major bonding issues that were previously unnoticed. While the rebar and lights were all bonded well, the equipment in the mechanical room wasn't bonded at all. I noticed some corrosion on the handrails that went in to the water and on our lane lines cables. Once we bonded every metal piece in the mechanical room the corrosion reversed itself and we haven't had a porblem yet. I should add that we've installed some sacrificial anodes as well (zinc).

In your case it sounds like your cover motor wasn't bonded at all, and maybe your light that is corroding wasn't bonded either. In most cases, building code requires binding wire to be non-insulated, heavy copper wire installed outside of a conduit where you can see it unless it is poured in to concrete (like your deck and pool shell). If you don't have a large bare copper wire connected to your cover motor you need to have a pool professional or electrician bond it porperly. Your light may be more difficult to remedy but have your local pro take a look.

The LSI will also play a huge part in corrosion as well.

Good luck.