View Full Version : TDS Readings

05/19/2014, 01:24 AM
Just thought I'd ask question on here about recent TDS findings. Both myself and a friend have recently purchased new RO Units (been running a month actually) I have also fitted a new 3 probe online meter to my own unit and both my friend and i purchased new TDS handheld testers.

We both live approx 1 mile apart and our incoming water is approx 360 TDS.

My unit (rated 200gpd) has 2 blue membranes (boosted by booster pump at 60psi) and the usual 3 pre filters plus 2 DI Pods (Resin changed 1 month ago). Pre DI my probe reading is approx 12 TDS and after DI it is 0.

My Friend just runs a 50 gpd low pressure membrane (with no booster pump/inline TDS meter) and no di unit yet. Yesterday we both tested our water with our 2 handheld testers with his reading 22 and mine reading 20 on his units water sample. When we tested my own we both got a reading of 5. I am therefore pretty sure we both have pretty accurate measures.

My question is really about the achievability in this hobby of regular 0 TDS? I would also find it quite alarming to contemplate just what local LFS are selling and was wondering what you guys think? Please feel free to comment on how to improve if possible? Since as Mr Saxilby says "we don't look after fish or coral we look after water" This is regarded as an essential part of the hobby.

05/19/2014, 02:47 AM
I measured mine from BRS unit and it was 0.. I thought my machine was broken. I measured it at least 5 times, youtubed it, and measured more.. machine stayed on 0. Then i realized i'm an idiot and tested it on outdoor water. It was reading 30+. measured the RODI water again, 0.

05/19/2014, 08:54 AM
I'm not sure exactly what you are asking but I think this is what you are after: First you said your RO/DI water tested zero with your in-line TDS meter, then you said your water tested 5 with the hand held unit if I am reading your question correctly. I would first advise you to calibrate all the TDS meters you are using. If the new RO/DI water you produce is still showing 0 TDS, then your storage container is leaching into your water. As to your question is zero TDS achievable, absolutely yes.

05/19/2014, 09:20 AM
Membranes usually acheive a 95 to 98% redution in tds when they are functioning properly. Di resin does the rest; post di water should be 0. Using two in line di cansiters with a tds meter in between is a good way to know when to change out the first one without post di tds getting into the tank.

05/19/2014, 10:31 PM
I've been at 0 tds for three months now, testing with two different handhelds. The key is to only make large batches of water (10+ gallons at a time) and flush religiously.

05/20/2014, 10:50 AM
Cheers guys, interesting comment re probe between di cannisters - never thought of that one.

05/20/2014, 01:46 PM
I use 2 di cansisters in line. A double probe meter keeps one probe at the input to the second in line canister/output of the first . The other probe is at the output at the output of the second . When the the input to the second reads more than zero; I change out the resin in the first and rotate the second into first position with the newly filled cansiter in the second position. This way, there is no tds after the second canister. It's a good way to tell when resin is exhausted in the first canister and to avoid premature changes or risk of post di tds getting through..