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Corey Price 
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 Topic: TDS Creep? Huh?
Posted: October 18 2006 at 2:05pm |
I tested my RO water out of the storage tank and found it to read 90 ppm on Mark's TDS meter (thanks Mark). For reference, my tap water is 330 ppm. I thought that this must be one reason behind the out-of-control algae that has been bothering my tank. Well, after further study and a call to Air, Water, & Ice ( www.airwaterice.com) where I purchased the unit, I have found that my RO water may be suffering from "TDS creep". This is what I've found out:
1. TDS creep is a common problem with RO units that have frequent, short-duration on cycles. Apparently reverse osmosis membranes do not produce high-quality water when there isn't a lot of water passing over the membrane. For example, hooking the RO line or storage reservoir line directly to the sump will result in short cycles w/ poor quality product water.
2. TDS creep and low output can be caused also by low water pressure in the RO unit. For example, a system running at 35 psi (dynamic pressure) just before the waste line restrictor is much less efficient than if the pressure is above 50 psi (dynamic). (I can't imagine whose problem this is also...  ) There will be some head (pressure) loss between the line in and the restrictor, but usually not more than 5 psi.
Some of the possible solutions include:
1. Use a RO top-off storage reservoir and fill it less frequently, activating the RO unit for longer periods.
2. Use anti-TDS-creep devices that allow a reservoir to fill in one drawn-out cycle instead of short cycles. The unit can be totally DIY.
3. Use a "permeate" pump. Such a pump can be purchased readily, uses no electricity, and boosts RO product water to waste water ratios to more than the abysmal 1:5 ratio.
The TDS creep in systems can be quite noticeable, (like mine) but it doesn't necessarily mean that the membrane is toast.
So all you out there that know this already, great. I'm just hoping to pass some info along for those of us who don't know this. I think it's logical, but many times I just assume that the water from the RO filter is great w/o really knowing that it's great (or not).
Please help me add to this post if you have more info. 
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Corey Price
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Posted: October 18 2006 at 6:42pm |
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So how does one test for TDS creep? Simple: Let the RO filter run for an extended period of time. Test water at startup and then after it has run for a while. In my case, test the water out of the drinking water storage tank, empty the tank, and test when the tank has filled back up. If you get 80 ppm before emptying and 15 ppm after, you know you have a problem with TDS creep.
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jfinch
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Posted: October 18 2006 at 7:35pm |
Which is one of the reasons why I use the "pump up" auto top-off system that I use. http://www.utahreefs.com/forum/forum_posts.asp?TID=1770
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Shane H
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Posted: October 18 2006 at 9:37pm |
Corey,
Thanks for posting this. I think many people may have this problem and not even know it. I have a habit of testing my tds once a month. It is one of those things that "creeps" up so slowly that it can be easily overlooked!
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Mike Savage
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Posted: October 18 2006 at 11:00pm |
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Corey, great info, thanks!
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Aquarium Creations
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Posted: October 19 2006 at 10:30am |
hmmm kinda weird, i test our R/O water at the store every week and we are around .003-.005 very interesting info..
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Corey Price
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Posted: October 19 2006 at 1:40pm |
My RO filter is directly connected to the sump top-off. So my thoughts to help this situation are to get an electric solenoid valve, put it in the line from the house water to the RO filter, and turn it on at night using a timer. The storage tank that's mainly for drinking water would be plumbed with a one-way valve to prevent it from draining into the sump, but still allow it to be used for drinking water. The sump could be then topped off from a reservoir, allowing me to dose kalkwasser directly.
The whole system would be filled nightly during a two to three hour time. The solenoid would prevent the RO filter from turning on otherwise.
What do you think?
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GARFVolunteer
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Posted: October 19 2006 at 6:27pm |
Here is a link to a top-off system I would like to build some time. http://reefcentral.com/forums/showthread.php?s=&threadid=275455 It is kind of a mechanical version of Jon's and was designed to reduce the effects of "TDS Creep".
I just need to get the planning and zoning committee (also known as the lovely and gracious Monica) to approve it.
Thanks,
Scott
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President Idaho Marine Aquarium Society
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"How do you make poor people rich by making rich people poor" Rush Limbaugh on Obama taxes
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Corey Price
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Posted: October 20 2006 at 8:49am |
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Very interesting, Scott.
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Mark Peterson
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Posted: October 21 2006 at 5:50am |
I believe it has a lot to do with the quality of the membrane.
I also believe that a well designed and brightly lighted RDP Refugium actually resolves the problem. The TDS on the water coming out of a Kold-Steril water purification unit is attrocious, yet the one which feeds water to a certain 180 gal tank that I know of, seems completely flawless.
Be careful not to make more of this than it really is.  A little extra stuff in the water is only one of five reasons for undesirable algae growth.
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Adam Blundell
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Posted: October 23 2006 at 8:47am |
I agree with Mark. Look at all the great tanks out there run with tap water. What are you worrying about?
Adam
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Corey Price
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Posted: October 23 2006 at 1:23pm |
Well, I've never been one to use unscientific methods such as the Blundell "finger-in-the-water" salinity test, and I'd like to get a handle on my algae problem.
However, I don't think testing any trace element regularly is very fruitful at all, so you got me there, Adam. Just calcium and alk for me. A wet thumb in the air is an okay decision-maker on many things for me.
My thoughts are if you're running RO, you should be getting better to really great filtered water, not just mediocre filtered water. I'm not interested in distilled ultra-pure water, so I do realize it's all in your point-of-view. Also, different municipalities will have different water quality. I have clear filter housings, and you should see my sediment filter- it was white, and after 6 months, it has turned completely brownish-black. Yuck.
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GARFVolunteer
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Posted: October 23 2006 at 5:24pm |
 Adam Blundell wrote:
I agree with Mark. Look at all the great tanks out there run with tap water. What are you worrying about?
Adam |
Not all tap water is the same... Implying it is, is kind of like saying all anemone fishes are clown fishes.
GARF has great tap water but their source comes from an area where there is no farming up stream so the chances of nitrates and phosphates are lower.
I use to have a 1 in 4 chance of having good tap water since my water use to come from 4 different wells. It still does come from 4 wells but there is a huge storage tank that they all dump into. My water tests high in silicates and phosphates. I am surrounded by farm land that has been turned into subdivisions.
Tap water at Cascade Raft & kayak had 40ppm nitrates last summer and all drinking water is RO. However this summer, the nitrates were undetectable. The thought is with all the rain we had this spring the nitrates were flushed away.
The person that got me interested in the hobby has, a well in the middle of farm land but his tests low for phosphates, silicates and nitrates. He does not use an RO unit.
Thanks,
Scott
Edited by GARFVolunteer - October 23 2006 at 5:25pm
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President Idaho Marine Aquarium Society
A fair and biased reef hobbyist
"How do you make poor people rich by making rich people poor" Rush Limbaugh on Obama taxes
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