RO/DI Unit and TDS meter

[Fishguy2727]

I am considering getting a RO/DI unit. I could definitely use it on my reef and I am considering freshwater stingrays again. I found a no-name unit on Ebay at a 'too good to be true' price. It is 100gpd, 6 stage RO/DI (2 stages are DI) at under $100 shipped. The seller has 99.7% positive rating with thousands of sales. It puts out 0ppm water (according to feedback, not just the seller). I know you get what you pay for, but this is all I can pay for.

If I did this I would want to get a TDS meter, even if it comes with one. This way I can doubel check the water coming out. I haven't used a TDS meter before, do they need any calibrating? We have one at work and I saw the owner use it, he just turns it on and reads the meter. It is one that made for checking the input and output water on a RO system inline.

I just want to make sure I am getting everything covered.

I know it is always risky to get no name products at prices like this, but is it THAT bad of an option?

[Dave66]

Fisgguy,
All electronic meters need calibrating, but it's far from rocket science calibrating a meter. Once calibrated you can use it for some time; between a few weeks and a few months, before it needs calibrating again.

You get what you pay for on RO/DI, like anything else, my friend. Sounds like a Chinese knock-off at that price. Trouble with cheap RO/DI is the membranes; they are so low quality you'll end up replacing them sooner rather then latter. They probably use discount cellulosic membranes, which clog in a hurry. If you buy that unit, replace the RO membrane with a TFC (Thin Film Composite) membrane, as properly maintained (regular back flushing) you can get years off a TFC membrane.

I can point you toward TDS (aka Conductivity) meters if you wish via PM. Decent ones aren't very expensive.

Dave

[Fishguy2727]

I found a bunch of TDS meters on ebay.

So I can replace the cheapo media and membranes with high quality stuff?

Can I replace different chambers for other media/membranes? I don't have any chlorine so could I replace one carbon chamber with a courser membrane or something like that? Or are the chambers designed in such a way that you have to use the intended media/membrane?

[Fishguy2727]

Actually the post specifies TFC (Made in U.S.A.).

I know it is definitely not the best on the market, but it looks like the best option for me.

Anyone else?

Anything else I may be missing?

[kaybee]

So I can replace the cheapo media and membranes with high quality stuff?

Yes. Most RO/DI housings/chambers and the various filter medias are universal. After it's been expended you could probably replace the membrane with a quality one (Dow Filmtec, etc). Excluding the membrane housing are all other housings/chambers vertical?

Can I replace different chambers for other media/membranes? I don't have any chlorine so could I replace one carbon chamber with a courser membrane or something like that? Or are the chambers designed in such a way that you have to use the intended media/membrane?

They can be changed out. You can opt for smaller micron filters (e.g., replacing the 5-micron sediment filter with a 1 micron or 0.5 micron sediment filter, etc regarding the carbon chamber are you referring to the carbon block or catalytic granular activated carbon (GAC) filter media? (the latter is designed specifically for the purposes of removing chlorine and chloramines).

You can do without the GAC if your water source doesn't contain chloramines or chlorine but you will probably want to keep the carbon block to protect and extend the effectiveness of the membrane which is down range from it (from heavy metals and other solids which can damage the membrane).

[Fishguy2727]

Sounds good.

[kaybee]

Regarding the TDS meter, TDS calibration fluid is fairly inexpensive (~$10), but most are calibrated at the factory and are pretty accurate right out of the box.

The TDS meter will be used to test the TDS of the source water and RO output (which will give you an indication as to when your membrane requires replacement), as well as testing the final RO/DI out put (to determine when to replace the DI resin).

Generally the filters and resin will last about 6 months, give or take depending on how much water is made and the TDS of your source water. The membrane will be effective for 2 to 3 years (again, depending on water production and TDS of the source water).

[dmagerl]

Do you really need a TDS meter if you already have the capacity to test for GH and KH?

I have an RO unit for drinking water since I am on a well. Several of my friends have one too.

In all cases I can take my testing kits and measure GH and KH of the RO output and it corresponds really well with the TDS meter. High TDS = High KH and GH.

[labnjab]

With saltwater you want exactly 0 tds, so you would want an accurate measurement so a tds meter would be the only real way to go

[Fishguy2727]

TDS is a little different from GH or KH, and more accurate.