RO/DI high TDS after start up?

[baker89]

Hey guys I'm kinda confused. I first noticed a problem about a month ago when algae started to grow in the tank so I checked my RO/DI and sure enough I had about 45 TDS coming out of it. So I changed the 2 carbon, 1 sediment and 2 DI and that brought it down to 0 TDS. Problem solved but I checked the TDS today (about 3 weeks after I changed the filters) and I'm getting about 45 TDS again... So then I took a couple of reading (see below) and they didnt add up... So I checked again and my TDS had gone down to about 0-3TDS. So I turned it off put the cup in a sink with the TDS meter and ran the water through it. It starts at about 50TDS and then slowly climbs down after about 3-5minutes. The cup I use are these cheap dollar store paper cups (I dont think its the cups). Do other people experience this and/or do i need to do something about it. Also I noticed that my DI resin looks a little low... When I added it I filled it up but the water condenses it
(I assume) and now it looks a low think I need to top it off?

Other Specs:
Tap water: 118TDS
After Sediment and carbon: 97TDS
After Membrane: 25
After DI: 0-3 (after 3-5minutes)

Thanks guys,
Dennis

 

[eww]

Hey Dennis. I am pretty sure this is normal. I think it depends ont he RODI unit as well. I have heard that in most cases you want to discard the first few gallons or so each time you start it up for this reason, especially if you are making small amounts at a time. We try to only make 30-40 gallons each time we start up the machine and but dumps into a 55 gal barrel so if there is a higher TDS at start up it is drastically reduced and diluted because of volume in our situation.

 

[Boomer]

Who's TDS meter do you have ? Some of these meters are very touchy and need to sit to equilibrate and any movement and the reading will change.

 

[1fishkeeper]

Melev had a great write up on this over on Reef Addicts. What you should do is put a "T" right after your line that comes out of the RO membrain and before it goes to your DI. Open it up so the water flows through the "T" and can go down the drain or a bottle to water plants. Let it run like this for the first gallon that comes out of it. Then turn your valve to it goes to the DI. The big reason he wrote this up was because that high TDS water when first starting up will burn through your DI resion fast. This will give your DI a long life and keep your TDS going to your tank at 0. Well after a long search for it on Reef Addicts I cant seem to find it. But Im sure someone out there might know what Im talking about. I keep on telling myself that I need to do this so I dont go through my DI so fast.

 

[estanoche]

Hey Dennis!! Have you figured our what was causing the high TDS on startup???? I'm curious