RO/DI question
 

Finally picked up a TDS meter and the water is pretty good. 26ppm.
I have been running my 36 gal with treated tap water for 2 years. Mostly softies and LPS with the fish and things have been fine. I just bought a used spectapure 100 GPD RO/DI setup. Do I need all cartridges to deal with such low TDS. Which membranes should I use. Being that low, I am tempted to just use the treated tap water. Only because I don't really have a place to set it up at my home. Opinions please.

I have also been using treated tap water, although I don't have a TDS meter yet, I know the lower mainland water is pretty good. I think the benefits of the RODI would be less algae to contend with, if you have any...

I can't comment on whether you'd need all the different stages or not though.

How many stages does your set up have? The most basic way to run it would be a carbon stage & the RO membrane. The carbon stage removes chlorine which would destroy the membrane. In most cases at least one sediment filter is used before the carbon stage. This will keep the undissolved crud from clogging up your carbon stage. Sediment filters are cheap & come in many different micron ratings, so you can try a few different ones to see how they perform with your water. Solid block carbon stages will also have different micron ratings, so be aware of that. Also check to see if Yellowknife uses chlorine or chloramine to treat the tap water. If they use chloramine, you may need two carbon stages. My system came with a carbon block & a refillable carbon stage. I removed the refillable one years ago & now run two sediment filters of different micron ratings in front of the solid carbon stage.

If you have a DI stage, you may as well use it. With TDS as low as yours, the RO membrane itself should bring the TDS to 1 or 0 before the DI, so the DI media will last for years. Having the DI in there will help ensure that any remaining bad stuff is stripped from the water. Even with my set up (75gpd membrane) and incoming TDS of 210+, the RO membrane manages to get the TDS down to 0 before the DI most of the time. It seems to get to 0 faster in the cooler season (within 5 minutes) when the incoming water temperature is around 8 degrees C. I suspect your incoming water in Yellowknife is fairly cold as well. In my experience that works to your advantage in terms of TDS coming out of the membrane. Downside is, slower production.

When it comes time to replace your RO membrane, you might consider switching to a 75gpd. Production will be a little slower, but 75gpd is better at removing TDS than 100gpd. You'll need to replace the restrictor as well to match the new membrane. Again, with your low incoming TDS, you could tweak the waste water flow after your restrictor by adding a small ball valve & restricting the waste water further. Need to be a little careful about that, since you will be forcing more water through the membrane with the higher restriction & that may impact membrane life. The advantage however, is better good to waste water ratio & faster production. Incoming water pressure will also have a significant effect on how well, or poorly your system performs.

the one thing you need to consider is the fluctuating dissolved solids in your areas water. running through the full system takes out any possible spikes that may occur. As mike said if the water is fairly stable at 23 then all the cartridges will last longer anyway, I would use it all.

I think that I will go that way and use it all. With the low TDS it should last a while.

It is a 3 stage RO + DI , The water is indeed cold from the source. I believe we have 80 PSI entering the building, so sounds like enough pressure.
I don't see any restrictor externally but I have ordered an inline model. I will try and get the ratio down a bit if possible.

Thanks for the advice, I bought the thing so I may as well use every stage and have some nice clean water in this larger system.

Mike, if you'd like to drink the water from your new setup, plumb a T of some kind before the DI as it's a no-no to drink water that pure :wink:

The restrictor may be part of a fitting on your membrane housing or built into a flush/check valve. If it was sold to you as a complete working unit, it should already have one somewhere that matches the 100gpd membrane.

My TDS was 8ppm and nearly killed my tank with copper a number of years ago. Apparently with such a low TDS it "scavenges" more copper from the pipes than higher TDS water does. I tested my tapwater with a copper test kit and was amazed. Killed a number of inverts. I've been using RO/DI ever since. And still, even with such a low TDS, the first sediment filter gets dirty and the carbon is used up on chlorine. The RO and DI lasts me a long time though. Another thing to consider is you don't know what comprises of that 26ppm. You only know it's dissolved solids that are safe for human consumption, but that's about it. So to answer your question, better be safe than sorry, use RO/DI.

No worries, I like it right out of the tap.

I will have a better look, took it out of the box and made sure all the hoses were there. Even came with full canisters, must have added a few pounds to the shipping weight. LOL

I am starting to come to that conclusion, bought the dam thing, might as well use it. :biggrin:

Megalodon makes an excellent point about the TDS with regards to not knowing what those solids are. People get focused on high/low numbers & forget that even a few ppms of the wrong stuff are detrimental to your tank inhabitants. I've often mentioned on RODI related threads that people should get a water report from their utility. The utility has to provide this information, it costs nothing & even if you are using RODI system, it's still good to know what's coming in on your tap.

You mention the unit was shipped with full canisters? I assume that means there is water in them? If so, that's likely a good thing, especially for the membrane, since once a membrane is removed from it's original packaging, if it dries out, it's done. Before using the unit it would be wise to give it a good flush, perhaps replace the carbon & sediment filters & sanitize the housings. There are some pretty good instructions on how to do this on various vendor's sites like Buckeye Field Supply, Bulk Reef Supply & probably on the Spectrapure site as well. Spectrapure site should also have some instructions/specs for your particular unit, including info on restrictor location etc.