Butyl rubber liner tank

[DocMax]

I'd like to recive some informations regarding potable water storage tanks.
In a water treatment plant designed for Saudi Arabia we installed a hot deep galvanising tank for potable water storage. This tank has inside a butyl rubber liner.
Now after few months the tank has some leaks.
I don't know if this leaks are caused by the free chlorine in the potable water that can oxidize the butyl rubber liner.
I saw the some rubber samples, the color was brown (the original was black) with larges brown stains, the rubber looks like an feels like hard.
Anyone could give me some details or had similar experience?
Best Regards
DocMax

 

[SMF1964]

Is there any water treatment chemicals that are going into the water prior to storage in this tank? I'm thinking excessive chlorination might be causing the butyl rubber to deteriorate maybe?