How high TDS before replacing RO/DI Filters?

[bikerfish]

I'm watching my TDS meter slowly creep up as the weeks go by on my RO/DI system. Last night the output was hovering at about 20-25 ppm, with the input at about 300.

How high is too high? I haven't noticed any change in the aquarium, but obviously the water is less pure than when it was still at zero.

I think the norm is to change them every 6 months, but it hasn't been six months yet (closer to 4).

Thanks

 

[gmax]

Do you leave the unit in "always on " mode? Or forget and leave it on frequently? Or do you do a lot of water changes or otherwise have larger than normal water usage?

Six months is just a guideline. A little like 3000 mile for oil in your car. Hard usage might yield a need for more frequent changes.

I would say that your filters need to be changed, your TDS reading will start yielding nuisance algae in your tank if it has not already.

 

[robertbeardslee]

My 6 stage 100GPD RO/DI reads around 4 on the TDS meter and it is about six months old

 

[waterbeing]

@gmax wrote:

Very true. Time is only a guideline for 'normal' usage...whatever 'that' is. It is really a pretty useless measure because of soooo many other factors (amt of top off/day, amt for water changes, amt for drinking, amt of tanks, etc) . Measuring input/output TDS and gallonage produced/used should really should be the guide, not time. :?

Bikerfish,
Based on what you are showing above, you may even be leaching TDS back from the DI to the water itself. I'm assuming your 100GPD membrane is a 98% rejection, which in my experience will actually yield about 90-95% when new. So... 300 TDS input * 5-10% let-thru = 15 to 30 TDS output from the membrane and *before* the DI has even touched it. Since it's reading 20-25 TDS after the DI, it is probably making the water worse (reverse leach) or at the very least not helping much/any at all. Since your input TDS is *relatively* low to start with, your DI probably will last quite a while (in terms of gallonage...not time). I would definitely change it at this point and measure your membrane input and output TDS by itself while you're doing so, just to be sure the numbers above are relatively correct.
I've become more conservative in what I'll let go for awhile myself. I used to let it rise to 10-17ish before I changed, but since we were going through so much of it due in high input TDS, I've tried to start changing more at 3-10ish. JME and HTH

Doug

 

[bikerfish]

Guess it's time to order new membranes.

It's not on all the time. I fill 5g jugs and keep them for water changes or refilling the auto-topoff. The RO unit is too far from the aquarium to make it practical for a direct connection.

But, I've been creating 25-30g per week, so it has probably run roughly 5-600 gallons through the system. I know, I should have written down when I installed it, but it's a new piece of equipment for me and I didn't think about it. I'll try to figure it out from my checkbook tonight. Maybe it's been longer than I thought, but I don't think it was cold outside when I installed it. :roll:

 

[kwl1763]

I change mine when it hits 3.

When is largely a matter of preference but I would not wait once it gets to 10 for sure.

It depends on your what the 5 is composed of if you'll actually see a difference. If the 5ppm is mostly phosphates (my case here) or nitrates then you'll notice but if it's something much more benign like a harmless metal then you wouldn't notice even at much higher levels.

Changing the prefilters every 6 months is a good idea but let the tds of output tell you when to change the DI.

 

[ToddLaCo]

Also remember that if your RO/DI unit has been off for a while, even a short while, the water will get stagnant in the unit and yield a higher TDS reading. Make sure you discard the first gallon or so of water when the unit is first turned on and don't use that water to measure your TDS.

 

[melev]

@bikerfish wrote:

First of all, not the membrane. The membrane should be good for 3 to 5 years. The filters that hang under the RO system are what you want to change, and yes you should change them now since your TDS is so high in your area (going into the unit).

How exactly are you testing TDS? Is it a handheld meter? Has it been calibrated?

I change my filters before it hits 10. Usually before it gets higher than 7.

Check your RO water by collecting a sample in a clean cup after the unit has run for 60 seconds. Checking the TDS in your normal collection container is a good idea, to see if the container is still clean or if it needs to be disinfected. Some people have barrels of RO (or RO/DI) water that read 50 or higher because their barrel is dirty. I use the Ozarka / Sparkletts water cooler jugs and they always test between 0 and 1. I've been using them for years, and they stay clean. I always keep them capped, empty or full. This has worked out great.

I've seen the magic number '600 gallons' bounced around quite often as the time to change filters. So if you are producing 100g a month, they would last about 6 months.

And regarding hooking up a RO/DI directly to the sump, please read this article:
http://reefkeeping.com/issues/2007-05/ml/index.php

 

[bikerfish]

I'm using an in-line dual TDS meter that I bought from Freshwater Systems. I'm not sure how to do a manual check with that. My water is stored in jugs that are the 5g cubes that come from the LFS originally. But like I said, I'm testing the TDS before it gets to the jug.

Now that I'm home and can check my log, I see that I bought the RO/DI unit Jan 28 and hooked it up the first week of February. So it's been running closer to 5.5 months. Longer than I thought! Time flies I guess.

Marc,

Thanks for the article on the dangers of hooking up RO/DI direct to the sump. I didn't plan to do that, since I'm happy with my big dogfood container of topoff water and an ATO switch, but it makes good points. I didn't think about my sump needing to have space for everything the container could pump in. I might have to lower the water level in the sump slightly so it can handle it (max would be about 10-11g coming in).

I just ordered replacement filters from you. Hope they're in stock!

 

[melev]

You might get them tomorrow. I'll email you with the tracking number.