My RO/DI Unit TDS Test

[drama07]

Hey,

Just replaced the sentiment & Carbon Block filters and had the opportunity to test out the water. I used a Hanna handheld TDS meter. Here are my results!

Water output from City Tap

1st trial: 162ppm
2nd trial: 165 ppm
3rd trial: 165 ppm

Water Output after both filters (before RO)

1st trial: 171 ppm
2nd trial 173 ppm
3rd trial 172 ppm

Water output after RO (before DI)

1st trial: 76 ppm
2nd trial (increased waste output): 28 ppm

Haven't tested water after DI, but will soon.

Is 28ppm okay coming out the RO membrane?

It's odd that the water TDS is higher after going though the filters. I did flush the new filters until I got 5 gallons.

I require opinions

Thank you

 

[aquaman67]

IMO your water out of RO should be <10 ppm.

It may get there as you flush the pre filters more. The carbon has fines that will get flushed off.

What type of RO membrane do you have?

165 - 28 = 137

137 / 165 = .83

A good ro membrane should be .98

.96 at the worst.

So 165 - 7 = 158.

158 / 165 = .96

So I would shoot for less than 7 out of the RO membrane.

You will be burning up a lot of DI resin if not....

 

[jcabatu]

this is either a failed membrane or time to replace.

I purchased the new vertex 100gpd RODI and was getting 28-40ppm after two months. I called Marine Depot to report my findings and they told me that if the membrane had dried up, this would cause it to fail. they sent me out a replacement and have not had problems since.

If you are getting anything less than 90%, you should consider replacing it.

 

[drama07]

@aquaman67..

It looks like letting it flush out has decreased the TDS. Now it reads 11 ppm.

@jcabatu

I doubt the membrane has failed. I only had it for a year and haven't really used it as much for it to loose its efficiency.

 

[Toddrtrex]

Really need to know what RO membrane you have. They all aren't rated the same.

In general, should get 96-98% rejection rate from a 75 GPD one, and 90% rejection from a 100 GPD one --- again this is in general.

Assuming that you change the pre-filter and carbon every 6 months, and keep the RO membrane wet you should get 2-3 years of use of it with your starting TDS, and perhaps longer.

 

[Newreeflady]

try to increase the flow to waste. I have approx the same tds from the tap and get only 3ppm out of the RO. Also, don't test the RO water until it has run for 5 mins as it tends to be a bit dirtier for the first few mins. Let it run for 5 mins, then collect some RO, then test.

-a

 

[drama07]

Yup! Increased the waste flow and let the water run for a while. It reads 6 ppm and I'll stay at that.

Not sure what type of membrane. I forgot. But if you know what the AquasafeCanada units are, then that is what I'm currently using.

Thank you for the help.

 

[Newreeflady]

Great, glad to hear it.

 

[SpectraPure]

to echo quaman67-
less than 96% is a reasonable time to change. Why? a 2% decrease in your rejection rate cuts your DI life in half as your ionic load is doubled. or conversely, a 2% rejection improvemnt doubles the life of your DI section.
bruce