Arduino + PH probe in Aquarium. Ground Loop. Please help.

Hi what about this optocoupler:

Does it will work?
And I have to buy 2 of these, on for Rx and other for TX.

I also said that there are some RS232 IC's that do this isolation. Can you point me any that i can find on ebay?

Thanks.

Edit:
Fund this:
http://www.ebay.com/itm/1x-MAX251EPD-5V-Isolated-RS-232-2-Driver-2-Receiver-MAX251-/110753204175?pt=LH_DefaultDomain_0&hash=item19c967c7cf