how to lower TDS level?

[NVTE]

I make lot of RO already and get about 19 ppm TDS. How to bring down those RO water's TDS ?

[nava405]

Originally posted by NVTE
I make lot of RO already and get about 19 ppm TDS. How to bring down those RO water's TDS ?

more filters or new filters... and i think you need RO/DI not just RO

[Left Coast DJ]

http://www.airwaterice.com/c=CXPJEqR...qh/category/1/

[epicfish]

RODI.

[reef_doug]

With a TDS that high, you may have not changed the sediment and carbon block and the membrane could be shot.

A good working RO of about 7 ppm followed by DI should bring it to 0 or less than 1 ppm.

[HenryTran]

at what number should you start changing the filters?

my tds is reading 3, should i change it soon?

[reef_doug]

Is the 3 TDS after RODI or just RO?

[HenryTran]

after RO/DI.

[Bebo77]

i let my water go to 20 before i change filters.. but i do change the sediment filter ( .5 micron) every month...

[CW from the OC]

Letting your TDS rise after the DI is a mistake, because it starts to preferentially release bad stuff. Often the first things to be released in large amounts are Ammonia and Silica. I don't think letting it rise to 1 or 2 is a problem, but I do think letting it rise to 20 is.

As an example, I recently forgot to change out my DI, and the TDS going into the DI cartridge was at 8. The reading coming out was at 10. It actually went up.

For factual backup, refer to this article by Randy Holmes-Farley, towards the bottom: http://www.reefkeeping.com/issues/2005-05/rhf/index.php

[frogiii]

doh~~ really? my TDS is reading around 50ppm. My RO unit is brand new just bought from Costco when BeBo post this RO unit no water waste system. is my TDS meter bad? also, from someone's thread that leads me to buy this : ) anyways, i though 50ppm was okay until I see everyone has it less then 3 or 5 even 20 what the heck??

[HenryTran]

my tap reads 287 and after ro/di it reads 3. i would check with another tds meter to confirm that you have 50. for a new unit, that is awfully high.

[d0cdave]

50ppm is bad... worse than bottled water in most cases. Those no waste filters are good enough for drinking water but I wouldnt recommend them for our uses. Maybe adding a DI stage and a prefilter might help.

I have a standard (but beefy) RO filter from a local water softener company... 3 stage. I still have a TDS of around 5-7 with 4 year old membranes. Granted I only run nanos and make tea/coffee every morning (1-2 gallons of use a day).

[frogiii]

Could it be my $10.00 TDS meter isn't reading correctly? my water is ran through water softner system too.

[NVTE]

so you think I should change the Sediment and Carbon filter? what is the size of Sediment you guy recommend ? .5 micron or bigger?

[d0cdave]

The softener won't make much difference in tds unless all dissolved solids are calcium based, which usually isn't the case. My water is over 400ppm tds AFTER my softener.

[golfish]

Originally posted by frogiii
Could it be my $10.00 TDS meter isn't reading correctly? my water is ran through water softner system too.

Bingo!! its funny how so many people put so much trust in a cheapo meter...I think their a fair tool to see change only.

Then again, if your using one of those "no waste water" units your readings might be right. I can't see those being as efficeint at TDS removal.

Originally posted by NVTE
I make lot of RO already and get about 19 ppm TDS. How to bring down those RO water's TDS ?

Can you pony up a little more info..

1) TDS of water going in?

2) What's the GPD rating on your your unit?

3) How old is the membrane?

4) 19 is off the RO, right? Not the DI?

5) What's the TDS reading off the DI?

[reef_doug]

If you have Chloramines especially, don't forget to stay up on the carbon blocks to save the costly membranes.

[BuckeyeFS]

A good rule of thumb is to replace your sediment filter and carbon block after six months. A more precise way to maximize the useable 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. The Matrikx+1 (“Chlorine Guzzler”) for example will remove 99% of chlorine from 20,000 gallons of tap water presented at 1 gpm. 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 its 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 dependant 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 to 3 ppm, 5 ppm, and higher, 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 then would otherwise have been the case. Sometimes the problem is poor quality resin – remember that all resins are not created equal!

Russ