RODI Questions

[wardda]

Hello,

I have had my RODI system for about 10 months now, supporting a few tanks, I make about 20 gallons a week on average with it. I have a 7 stage 100 GPD system (5micron PP sediment filter, 2 x 5 micron coconut carbon block filter, 100 GPD RO Membrane, and 3 x 0 PPM DI filters).

My question is how often should I be replacing each of these filters, (how do you know when they are bad, is that what I need a TDS Meter for?) Then are there varying grades of filters or are they pretty much all the same? Where do you buy yours from?

My current concern is that on my tanks that don't have a skimmer on I'm getting green water even under low bio loads (two salt water tanks and 1 fresh water). My Nitrates and Phosphates are both coming in at 0PPM out of the RODI, does that mean that the filters are working great or are there other things I should be checking?

Please school me on the ins and outs of RODI :-)

Thanks,
Dan

[PoeticInjustice]

You definitely need a TDS meter to check the efficiency of you RODI Filter. Do you have a pressure gauge installed on it now? You would need the latter to check the condition of your sediment and carbon filters.

[wardda]

So for the TDS meter will something like this work? http://www.spectrapure.com/St_quality_p7.htm (the 29.99 version?)

[shifty51008]

that TDS meter will work fine.

you want to change your prefilters every 6 months regardless on how much water you make because of bacteria, your DI can be changed when your TDS starts to rise, and your membrane when your pressure starts to drop or your rejection rate starts to go lower.

[no1b4me]

they both are nice tds meter but the one i have is the first picture, i am using the same one especially when it installed inline, you can check it any time. my tds been 3 yrs and still working good as i typed. would be nice you can add a pressure gauge so you know your water pressure in the range. if less pressure you will waster alot water and if it is too much, you will go through alot media and filter.

[wardda]

Ok, some additional questions:

1) Where do you usually buy your filters is there a good online store, I got my system from purewaterclub.com, is that ok or are there higher quality filters I should be buying?

2) Change your DI when TDS start to rise, what is a good TDS or is it when your TDS start to move up towards your non filtered water levels?

3) Pressure guage, what are good/bad pressures and is that measured between the tap and the first filter?

Thanks,
Dan

[mbg75]

When Tds is no longer 0, change the Di resin.
Pressure gauge goes after the pre-filter, but before the membrane

Sent from my ADR6300 using Tapatalk

[PoeticInjustice]

Originally Posted by wardda

So for the TDS meter will something like this work? http://www.spectrapure.com/St_quality_p7.htm (the 29.99 version?)

You can have that but the one I have is handheld like this:

http://www.ebay.com/itm/TDS-Meter-HM...item336cfb3b51

That one in the link is actually a pretty nice deal as I bought mine for $25.79

[Palting]

1. I usually buy mine from Bulkreefsupply .com, but only because that's where I bought my unit.
2. The final TDS in my output water is zero. I change my DI resin when it goes higher than 1. The TDS after my membrane and before the DI resin is 1-2. I will change the membrane when the TDS there goes above 5.
3. It depends on the unit and it's requirements, as well as where the pressure gauge is. My gauge is after the prefilters and before the membrane, and the manual states that the pressure should be above 35psi. Check your manual.

[PoeticInjustice]

^ I bought mine there too. Are you using the 1 micron pre-filters? Those are low TDS numbers.

[jeff@zina.com]

Originally Posted by wardda

1) Where do you usually buy your filters is there a good online store, I got my system from purewaterclub.com, is that ok or are there higher quality filters I should be buying?

Almost everyone is selling a Filmtec membrane anyway (and you don't want a cheaper one). About the only "better" membrane would be one from Spectrapure. Not that they're better, but they're pre-tested and you only get the top ones.

Originally Posted by wardda

2) Change your DI when TDS start to rise, what is a good TDS or is it when your TDS start to move up towards your non filtered water levels?

DI is changed when output water TDS goes above zero. Membrane is changed when TDS after membrane but before DI starts to rise. That means you need a baseline test to compare to. Inline TDS meters help here.

Originally Posted by wardda

3) Pressure guage, what are good/bad pressures and is that measured between the tap and the first filter?

Pressure gauges (yes, plural) go before everything and right before the membrane. You watch the difference between the two to determine when the filters are clogging.

Jeff

[Buckeye Hydro]

This (from our FAQ's) may help:
A good rule of thumb is to replace your sediment filter and carbon block after six months. A more precise way to maximize the usable life of these two filters is to use a pressure gauge to identify when pressure reaching the membrane starts to decline. This is your indication one or both of the filters is beginning to clog.

Also be cognizant of the chlorine capacity of the carbon block. A good 0.5 micron carbon block for example will remove 99% of chlorine from 20,000 gallons of tap water presented at 1 gpm. Some original equipment suppliers commonly provide carbon cartridges rated at 2,000 to 6,000 gallons.

Regarding your RO membrane and DI resin, use your TDS meter to measure, record, and track the TDS (expressed in parts per million) in three places:
1. Tap water
2. After the RO but before the DI
3. After the DI.

The TDS in your tap water will likely range from about 50 ppm to upwards of 1000 parts per million (ppm). Common readings are 100 to 400 ppm. So for sake of discussion, let's say your tap water reads 400 ppm. That means that for every million parts of water, you have 400 parts of dissolved solids. How do we go about getting that TDS reading down to somewhere near zero?

If you do some experimenting with your TDS meter, you'll note that your sediment filter and carbon block filter (collectively called “prefilters”) do very little to remove dissolved solids. So with your tap water at 400 ppm, you can measure the water at the “in” port on your RO housing and you'll see it is still approximately 400 ppm.

The RO membrane is really the workhorse of the system. It removes most of the TDS, some membranes to a greater extent than others. For instance, 100 gpd Filmtec membranes have a rejection rate of 90% (i.e., they reject 90% of the dissolved solids in feed water). So the purified water coming from your 100 gpd membrane would be about 40 ppm (a 90% reduction). Filmtec 75 gpd (and below) membranes produce less purified water (aka “permeate”), but have a higher rejection rate (96 to 98%). The life span of a RO membrane is dependent upon how much water you run through it, and how dirty the water is. Membranes can function well for a year, two years, or more. To test the membrane, measure the total dissolved solids (TDS) in the water coming in to the membrane, and in the purified water (permeate) produced by the membrane. Compare that to the membrane’s advertised rejection rate, and to the same reading you recorded when the membrane was new. Membranes also commonly produce less water as their function declines.

After the RO membrane, water will flow to your DI housing. DI resin in good condition will reduce the 40 ppm water down to 0 or 1 ppm. When the DI output starts creeping up from 0 or 1 ppm, you know that your resin needs to be replaced. Sometimes people complain that their DI resin didn't last very long. Often the culprit is a malfunctioning RO membrane sending the DI resin “dirty” water. This will exhaust the resin quicker than would otherwise have been the case. Sometimes the problem is poor quality resin – remember that all resins are not created equal.
Russ