What's your TDS Reading? Mine is...

[Anonymous]

...6PPM.

My RO/DI is a year old and I have only change the 1st stage sediment filter once. The input water has a TDS reading of 350PPM.

What do you guys think. Change the filters or hold out?

What's your TDS (input and output) ?

Louey

 

[marinelife]

I change mine when it hits 2PPM, Usually once a month for the DI and every other month for the rest

 

[reefland]

I have a dual probe TDS meter on my RO/DI unit. The post RO reads 5ppm and drops to 3ppm after about 20 minutes of use. The post DI reads 0 ppm. I change my pre-filters once the post DI hits 1 ppm and change the RO membrane when it no longer rejects 98% of the the source water TDS.

 

[Anonymous]

Hmmm. I sounds like I'm over due to change my filters. I think I'll change the sediment and carbon filters along with the DI cartridge. The membrane should last 2 or 3 more years.

Any others?

 

[SPC]

Posted by Reefland:

I have a dual probe TDS meter on my RO/DI unit.

-Rich, where did you purchase this and can it be used with any 5 stage unit?
Steve

 

[marinelife]

I have a dual probe TDS meter, it is just an Inline TDS Meter that Premium Aquatics sells

 

[reefland]

-Rich, where did you purchase this and can it be used with any 5 stage unit?

Yeah, it can be used with any RO/DI as long as you use the correct fittings. I got mine from Marine Ecosystems about a year ago.

 

[MiNdErAsR]

FWIW, you should change the sediment filter and carbon block at LEAST every six months, depending on source water quality. My TDS is 61 ppm out of the tap, and I change the DI cartridge when I get a reading of 1 ppm.

 

[reefland]

FWIW, you should change the sediment filter and carbon block at LEAST every six months, depending on source water quality.

Good point! I change my DI when it shows 1ppm TDS. But I change out my sediment and carbon prefilters every 3 to 4 months.

 

[IcantTHINKofONE]

What does TDS stand for and what is used to measure it?

 

[Anonymous]

What does TDS stand for and what is used to measure it?

It stand for Total Disolved Solids. It is measured in PPM (parts per million). It shows how much crap is in your water.

It is measured with a TDS meter that can be purchased for $25. Hanna is a respected brand. They are primarily used by reefers to tell when is time to change RO/DI filters.

Louey

 

[bpnc]

Mine is 170 going in and 14 coming out. It is a Kent Marine Full Size 50 GPD with all new filters and membrane..I have made about 50 gallons with it..

I am using a new Hanna TDS 1 meter.

Why it not lower than 14? Do I need to a DI to the unit?

 

[Anonymous]

Mine is 170 going in and 14 coming out. It is a Kent Marine Full Size 50 GPD with all new filters and membrane..I have made about 50 gallons with it..

170 in 14 out is 92.3% rejection. A properly working RO unit is supposed to reject 95-98% of all impurities. I think 98 would be expected from a brand new one. I wonder if yours need a little more breaking in? I don't know of they require breaking in and I didn't have a TDS meter when I first got mine.

I think you should add a DI cartridge, though I'm not sure how to add it? Mine came with DI.

Any one know if RO's need to be broken in?

Louey

 

[IcantTHINKofONE]

I have a Kent Marine 60-GPD Hi-S system and the instructions say to throw away the first 12 or so gallons.

 

[EmilyB]

I have just ordered a TDS meter. I don't understand how you know if the out reading is due to the cartridges needing replacement, or the membrane ? Are you taking measurements from different places in the unit itself ?

 

[reefland]

Emily - that is exactly right. Measure your tap water, measure the water coming out of the RO membrane and measure the DI water.

You should have 98% or higher rejection on the membrane. And your DI output should be 0 PPM TDS.

How simple this is depends on the TDS meter you have. I have a dual probe TDS meter that monitors the RO and DI side with a nice LCD readout. When my membrane was new I got 3ppm TDS water out of it. Now nearly a 8 months later I show 9 ppm TDS which is still fine and better than 99% rejection according to my TDS meter. The DI cart polishes off the water to get it down to 0 ppm TDS.

What you need to figure out is when to replace the DI. I replace mine once it shows 1 ppm output. Sooner than most people, but better safe than sorry keeping my nutrients low as possible.

 

[gman2]

Reefland,

I'm going to ask a stupid question, but how do you calculate the rejection rate?

Also I like the idea of the dual probe you use. I looked at Premium Aqautics and did not see it. Do you by chance know the brand or have a link to it? Also how much if you know.

Thanks
Tony

 

[liquid]

Here's the dual TDS meter reefland uses:

And here's the webpage on Marine Ecosystems' website that talks about the TDS meter:

http://www.marineecosystems.com/DryGood ... otal-35882

FWIW, I'm planning on picking one of those up sometime soon...

Shane

 

[reefland]

I'm going to ask a stupid question, but how do you calculate the rejection rate?

If your tap water is 320ppm TDS and your RO output is 5 ppm TDS you simply do: 9 / 320 * 100 = 1.56. Then subtract that from 100 to get 98.4% rejection.

 

[ChrisRD]

If your tap water is 320ppm TDS and your RO output is 5 ppm TDS you simply do: 9 / 320 * 100 = 1.56. Then subtract that from 100 to get 98.4% rejection.

BTW, Rich intended to say 5 / 320 * 100 = 1.56 for the above example.

Gman2, said another way that might be easier to follow:
If you had 320ppm at the input and 5ppm at the output, the membrane rejected 315ppm (320ppm - 5ppm). If you devide what you rejected (315ppm) by your original total (320 ppm) that indicates what percentage (in decimal form) that the membrane rejected. 315 / 320 = 0.984. You can then multiply the last number by 100 to express it in percent as Rich showed above to get 98.4%.

HTH