TDS Creep: How do you manage it?

[Sherman]

TDS Creep.

I'm starting to wonder if I made this term up (except I didn't). I can't seem to find any answers on how to avoid it, either on this board or any other of those major reef forums.

What are you doing to reduce/minimize TDS creep?

 

[mmkeeper]

Can you explain what you mean by TDS creep?

 

[zenn]

i'm also quite intrigued by this. I still don't know how the first bit of water get's contaminated if it's already been run through the system...or how much of it's contaminated. Those are some of the questions i'd like others to help out with.

 

[zenn]

Can you explain what you mean by TDS creep?

Sherman explained it to me as the first bit of water that sits in the RO/DI filter in between uses that gets contaminated. In order to avoid adding this water to your system, it's advised that you discard the first bit of water before introducing any further amount into your system.

 

[Sherman]

Yeah, pretty much. For those of you who have inline TDS meters, watch the TDS when you first turn on the water flow. It "should" be sitting at zero, and when the water starts flowing, it will increase. I've seen as high as 30 initially, then it works its way back down to zero. I'm not an engineer, so I can't tell you WHY the RO membrane does this, or perhaps it's a function of the DI and needing to be charged. Honestly, I don't know what causes it.

Anyway, the problem is that this initial "blast" of TDS happens every time you first turn on the water flow from your RO/DI. It's referred to as TDS creep, because where else is the TDS going but into your tank/reservoir?

So a fellow reefer (Weatherson) developed an anti-TDS reservoir. Another reefer (Brian Renegar) whipped up this diagram of what's happening. It's a pretty good illustration, so I won't go into too much detail. The idea here is that initial TDS blast only happens once per filled reservoir, instead of constant, as happens when the RO/DI is connected directly to a float valve in the sump:

I've heard from my best friend's ex-roommate's uncle's hair dresser's carpool buddy that Spectra-Pure now puts out an RO/DI that automatically dumps the first portion of filtered water down the drain before it starts producing, but I haven't verified this. Maybe someone else knows more.

Otherwise, is everyone just running their RO/DI line right into the sump/reservoir? If not, what's your setup? At this time, I manually fill my reservoir about once a week, and would love an automation idea, such as posted in the image above.

 

[wrightme43]

I am not testing this, or anything like that. I am just tossing out a thought. NOT knocking it.
That said.
In my mind it wouldnt it be better to have a very short term "creep event" like when the float valve cycles on and off 3-5 times a day?
Also does the benifit of Lower TDS outweigh the Benifit of non varying salinity.

 

[zenn]

i've got a tds meter but it isn't inline. I'm going to do some experiments to find out how big of a tds creep problem i have. I'm looking for a new way to dose kalk and to top offs automatically. So this discussion is important because it could change what i plan to do.

 

[LakeEd]

I was following another of DonW's "McGuiver" isums... and a large reason he is automating his RO/DI system is due to the TDS Creep. Figured it may be worth linking here;

http://www.reeffrontiers.com/forums/showthread.php?t=19249

 

[zenn]

i really need a fish room bad

 

[DonW]

Ive been talking about this for the past two years. Spectrapure puts out a $169 pdt gizmo and its no longer bs, amazing I should have got a patent. Tds creep is real and both types of systems are problematic. The fill the tank every few days system is fouling the tds membrane and the quick cycle system is fouling the membrane.
Both are easily cured. If your seeing it on a typical hm inline tds meter then you have it pretty bad. If your not seeing then you need a conductivity meter to test for it and its probably not all that bad but it is shortening the life of your membrane and di resin.

Don

 

[Sherman]

In my mind it wouldnt it be better to have a very short term "creep event" like when the float valve cycles on and off 3-5 times a day?

There will be the "same amount" of creep every time the valve is opened. So with 3-5 short cycles, the idea is you would get 3-5 times the TDS than you would if you were doing one long fill, as in a reservoir. The idea behind the illustration above is that you'd only open the valve once per however much the reservoir holds. For me, it's a 13g reservoir, and lasts me a week. For Weatherson it's an 18g reservoir (I think) and lasts about a day and a half. In the case of extreme evaporation like this (12g/day) can you imagine how often that float valve would be opening and closing in a normal day?!

Also does the benifit of Lower TDS outweigh the Benifit of non varying salinity.

The idea here is to fill a reservoir, so the salinity would be just as stable as if the RO/DI were hooked directly to your sump.

 

[Sherman]

Don, I just read through your thread. Great work and documentation, thank you. I'll read it more closely when I have even more time.

 

[DonW]

The idea behind the illustration above is that you'd only open the valve once per however much the reservoir holds. For me, it's a 13g reservoir, and lasts me a week.

I'd like to know who came up with this one? According to Dow this is worse than cycling the membrane. Shutting down the the membrane for more than 24hours is not good and after 48 hours the membrane shoud be disinfected. The membrane takes along time to recover from being shut off for 48 hrs alot more than 13 gallons so the membrane does not recover by the time you fill the tank back up and get progressivly worse each time. You can actually watch it get worse and worse with a conductivity meter.

Don

 

[zenn]

all this talk has me very confused. I had believed ro/di units produced clean water. Now you're saying there's all these other factors and that they don't necessariyly produce the same water quality i once thought?

 

[DonW]

all this talk has me very confused. I had believed ro/di units produced clean water. Now you're saying there's all these other factors and that they don't necessariyly produce the same water quality i once thought?

Dont stress. Were talking pre di here so the water going into the tank is just as clean as you were thinking. We all have tds creep but the di resin is taking care of it for us so the water leaving the di is 0 tds. The devices used to reduce the tds creep are just keeping the di resin from going bad quicker. They also make the membranes last a little longer. If your di consumption is low and your happy with how long your membranes are lasting, dont worry about it.

Don