Making chlorine?

[GTR]

Is there a chemical reaction that could produce measurable chlorine in a running system?
I know this is a crazy question but all other possibilities have been eliminated other than sabotage.

[Dan_P]

Electricity and seawater would do it.

Can you give more specifics on what you are thinking?

[GTR]

I'm still at a loss as to how I could measure chlorine in a system. RO/DI, mixed SW and NSW all tested zero. 6 other systems in the same location, some had more new water added than this system all tested zero.
This system is the only one equipped with a UV. It's a twin lamp unit and the lamps look like and HQI lamp, double ended. One lamp has been out for a couple of weeks but it was removed from the unit.
No electrical current was felt but we weren't looking for it either.

There was considerable stock die off in the system. Some looking as though they had gas bubble disease, bubbles in the eye and bubbles inside the fins.

Once the chorine was discovered prime was added and the carnage slowed then stopped.

First chorine test showed a trace, the next two tests each showed an elevated level over the previous one. Pool chlorine tabs as they dissolve come to mind.

We also use pleated filters but no one will claim to have changed them recently. Those filters are bleached. rinsed and then put in a Prime bath. I stuck my nose in the dry ones the day before this happened and there was no trace odor of chlorine.

[bertoni]

If it was chlorine, I can't think of any moderately credible source inside the tank.

[farfromsea]

The only thing I could think is if your municipal water source contained chloramine (like mine does). I'm a bit rusty on organic chemistry unfortunately but wouldn't chloramine allow for the presence of free chlorine in the tank? Anyways, perhaps the RODI water you used in the tank at some point contained chloramine for whatever reason but the RODI water you tested did not?

Second thought is that maybe someone did handle pool chemicals and inadvertently stuck their hand in a tank without proper cleaning.

Sabotage would be an unfortunate thing and reminds me of a story I read a while back about mercury poisoning at a LFS in Jersey

[OllieNZ]

Saltwater swimming pools use electricity to produce chlorine, definitely something worth checking.

[GTR]

This happened in a 3,800g capacity system.
Approximately 200 gallons each of RO/DI and NSW were added the previous day. Both of those holding containers measured zero chlorine and ammonia. Those perimeters are measured daily from the RO/DI at the output point anyway. Other similarly sized systems had similar additions with no impact.

[bertoni]

Which chlorine kit were you using and what was its sensitivity? Do you have GFCIs on the equipment?

[OrQidz]

I'm no chemist, but http://www.poolcenter.com/chlor has some interesting information about chlorine and salt water/electrolysis.

"Chlorine is produced by the electrolysis of salt water. When electricity is passed through 2NaCl (salt) and 2H20 (water), the atoms dissociate into Cl2 (chlorine) + 2NaOH (sodium Hydroxide) + H2 (Hydrogen). "

Since this is the only tank with the UV setup, that is a possibility I suppose. Plug the UV into a GFCI, see if it trips, stick it into a bucket of salt water, and see if you measure chlorine?

I guess the other thing you have to ask yourself is whether it's likely anyone would sabotage the tank and if so, does it make any sense that it would be that one? Obviously that might be a personal situation you might not want to go into, but is this one tank more accessible, or in some way a more attractive target of a saboteur?

[bertoni]

I agree that electrical currents can produce chlorine, but I've never heard of that happening in a reef tank. I agree that a GFCI test would be useful.