tds meter question

EmilyB · #1 06-27-2006, 08:17 PM

It's the RO membrane that is supposed to be ~95% efficient, the DI gets the rest. This is how you can test your membrane to know when you need a new one.

danny zubot · #2 06-27-2006, 08:31 PM

Does anyone know of a store in Calgary that supplies DI beads? If so, how much? Mine are 90% brown now.

Delphinus · #3 06-27-2006, 08:32 PM

I get a surge of TDS (post-RO/pre-DI) when I turn on my RO/DI that can be anywhere up to 150. It falls off quickly though, within 10 seconds usually it's down to zero. The post-DI is always zero - if not, the DI is spent and needs to be replaced.

I always kind of wondered if this TDS surging is normal (I have my RO/DI on only to fill my 50gal topup reservoir, about once every two weeks, otherwise it's off). It sort of looks like, judging by the comments so far, that this may not really be typical for others. Hmmm. Although maybe the way I use my RO/DI isn't typical..

EmilyB · #4 06-27-2006, 09:22 PM

I seem to remember reading somewhere that your RO/DI should be used at least once a week, maybe that was in my instructions - I'll have to check.

TheReefGeek · #5 06-27-2006, 09:25 PM

You get a slight build up of particulates when not using the RODI, using it regularly is good for that, and keeping the membrane in use is good too, you shouldn't let it sit forever.

Delphinus · #6 06-27-2006, 10:01 PM

I had actually been using my RO/DI directly to the float valves on my tanks and let them kick the solenoid on and off as required, but I found that I was exhausting RO membranes prematurely this way. At one point (you could even read about it here, there's a thread about it somewhere, I think from about a year ago) I went through 3 membranes in the space of a couple of months. So that's why I switched to filling up the reservoir, as needed, in one go (that's what was suggested to me anyhow). Maybe I should switch to a smaller reservoir - one that requires refilling slightly more often than the current 10 days it seems to offer me. Moving the float valve lower into the tank ought to do the trick.

TheReefGeek · #7 06-27-2006, 10:05 PM

I trigger my RODI once a day, I am still on my origital RO membranes, they are over 2 years old now, I haven't even flushed them out. I have gone through a few sets of the other filters & DI though.

My waste water production has probably increased, but I don't measure it so I don't know. Its probably time to replace my membranes.

Delphinus · #8 06-27-2006, 10:10 PM

At two years you might be getting close to needing to replace it. Then again maybe not. I think I got 3 years on my first membrane which is why I was so surprised at how finicky they can be after all.

Basically I wouldn't worry about replacing the RO membrane unless you get uncharacteristically high tds coming out. I.e., if you watch your tds then you'll know when it's time to replace it. I would get about 40-70 tds coming out which is still basically a tenfold reduction, so there was still function left, but still, obviously there's a problem if you get those kinds of numbers and not, say, 0 to 10.

I replace my prefilters approx. every 3 months.