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Re: [APD] Re: ro/di unit

Quoting Wright Huntley <whuntley at verizon_net>:

> The tds meter is the prime way to monitor general performance, but the 
> RO unit has essentially no ability to block small molecules, like 
> ammonium and chlorine. For that, they often use a carbon filter that can 
> fail in two ways. The flow can be too fast (contact time too short) or 
> the carbon saturates and allows "punch through." Don't throw your 
> ammonium and chlorine test kits away, as they should be used, once in a 
> great while, to monitor for the above phenomena.

It is a good idea to test that, but you should really just play it safe and 
replace your carbon filters every 6 months or so... they aren't very 
expensive. Not only can an exhausted carbon filter allow chemicals to pass 
through, it can release chemicals it has removed from water in the past and 
potentially release those chemicals in a higher concentration than what is in 
your regular water. 
> [A RO unit without a carbon filter is worthless for fish/plant tanks, 
> IMHO. I have seen them for sale, so beware.]

I believe the filter this person was looking at does have multiple carbon 
filters and sediment filters (in addition to the RO membrane). Good point 

> The tds meter will help you avoid osmotic shock and warn if the membrane 
> has failed (unlikely, if installed right). The other tests will warn you 
> to change your carbon filter before the tds changes enough to be 
> significant, I think (likely to be a regular mainenance procedure).
> Wright

A TDS (conductivity) meter is definitely a good idea with a RO/DI unit. 
Especially if you have a DI unit. That is the only real way to tell when the 
DI filter has become exhausted and needs recharging/replacing.

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