**NEW**RO/DI Question

I see many RO/DI units and I'm not clear on the stages.

What is the best stage RO/DI unit to get? Example 2,3,4,5 stage.

Are the filters interchangeable. What i mean is if you buy a 3 stage can you pick the 3 stages of filtration you want to have? If so what combo is best.

I am looking @ the Spectra Pure brand for an example. SpectraPure Customer Appreciation SALE! 20% - 50% off

 

IMO, 4 stages is good enough. Anything more and IMO, it doesn't do that much. What you want is a carbon filter, sediment filter, RO membrane, DI resin/cartridge. I use a four stage and have never had any problems. You do want to get full sized filters though, make sure of that.

 

Spectrapure builds excellent units. The CSP-DI is a great system and the MaxCap is the Cadillac of the industry.

Pay less attention to the number of stages and more atention to what each of those stages contain. Spectrapure does it correctly in that they use only high end filters which do a premium job of protecting the RO membrane so you don't have to add more "stages". Actually the word "stages" is something the low end resellers and importers use to make their low end low efficiency systems sound like whiz bang systems. They tack two low quality carbons together or two or even three little horizontal tubes with some DI resin bobbing around in them and call them "stages" so it sounds impressive.

In truth a single high quality low micron prefilter does a fantastic job of protecting the more expensive and more important carbon block so you don't need or want two carbons. Using Spectrapure as the example, both the MaxCap and the CSP-DI use a 0.5 micron, absolute rated prefilter so it traps 99% of everything 0.5 microns and larger so they cannot plug or foul the carbon block. Then they both use a 0.5 micron 20,000 gallon carbon block. Carbon is made up of billions of tiny microscopic pores which is where the chlorine is adsorbed. Cheaper systems use higher micron prefilters as high as 10 microns nominal rated (meaning they only have to trap about 85% of particles up to 10 microns in size and are allowed to pass even larger particles) so many partculates, colloidal materials and sediments get passed through and foul or plug the carbon pores. Since the first carbon is all but worthless at this point some add a second carbon block to do what the first one should have done, see how they add stages?

The multiple little horizontal DI filters do not hold 20 oz of DI resin for one and they are prone to short circuiting or channelling since the water is going to take the path of least resistance and flow along the bottom while the DI will try to float on top. Vertical DI canister are designed so the water enters the bottom and flows upward so all water and resin come into contact with each other so only a single cartridge is needed to be much more efficient and cost effective.

For a good reef quality RO/DI you want 4 stages, one 1 micron or less prefilter, one 1 micron or less carbon block, one 75-90 GPD RO membrane(Spectrapure starts with the industry standard Dow Filmtec 75 GPD membrane then treats it in a special proprietary process to improve its performance) and one full size vertical 20 oz refillable DI canister and cartridge. If you want to improve upon that the MaxCap adds a special dual DI system which greatly extends the life of the DI resins and is worth the cost difference in most cases if you make much water.

Yes, most vendors use industry standard 10" replacement filters. The best combination is the one that does the best job of protecting the RO membrane which is the workhorse and does 90-98% of the work. I already mentioned micron sizes above with 1 micron being the absolute largest you would normally want to go and 0.2, 0.5 or 0.6 microns being better. Personally I use a 0.2 micron absolute rated pleated prefilter which gives me 10x the surface area of a normal prefilter, a 0.5 micron 20,000 gallon carbon block, a 90 GPD Select series RO membrane and the MaxCap and SilicaBuster DI resins.

 

I couldn't have worded it more precisely. Except for the fact I use a 5 stage from the Filter Guys.

 

Except the order is wrong. You want the prefilter first, followed by the carbon block, RO membrane and DI in that order.

 

AZDESERTRAT, you have come through again. Thanks for spreading your knowledge of the subject. K+ to you. I know what i want now.

 

New question TDS

Good morning, I am getting ready to buy my RO/DI from spectrapure.

Both spectrapure.com and marinedepot have the 4 stage unit. Spectapure has a 4 stage built in TDS meter and marine depot's 4 stage does not.

So my question is what is a TDS meter and is it important?

 

A TDS meter is uberimportant. It lets you know how much stuff is still in the water and how much has been filtered out. That's important to know you've got 0 TDS (the usual goal of RODI), and it's also important for maintenance. You can figure out if you need to replace the DI or RO membrane with the info it gives you.

 

Speaking about TDS, do the probes need to get serviced. How do you clean them or what do you use to clean them?

 

It looks like the CSP-DI on Marine Depot comes with a push button putity monitor rather than a dual inline TDS meter?
Its a push button Go-No Go type monitor that does not give you numbers, just a red light green light type of deal.
I would stick with the CSP-DI in the sales flyer here:
SpectraPure Customer Appreciation SALE! 20% - 50% off

Plus its $55 cheaper!

Here are the calibration, care and maintenance instruction from HM Digital for all their meters.
http://www.tdsmeter.com/calibration_maintenance.html