ASO Valve and TDS meter

[asylumdown]

Don't know about the shut off valve, but TDS meters are relatively easy to come by. I use this one as a backup checker to make sure the TDO meter that's built in to my RO/DI unit is giving me an accurate reading: http://www.reefsupplies.ca/online-st...TDS-meter.html

I bought mine locally, I'm sure you could pick one up at one of the LFS in your area if you didn't want to have it shipped.