RO/DI quality issues

[jacksonpt]

I've been struggling with what I suspect to be bad RO/DI water issues basically since I set up my tank. I've got a 5 stage RO/DI system (Ocean Wave + 5 Stage 75gpd from the filter guys) with TDS meter. I replace the filters whenever I get a consistent TDS reading of 5 or higher.

It's been a nuisance since the beginning, but has compounded with a couple of other problems lately to really become an issue. I've lost a clam, my prized hammer colony is teetering, but it looks like my elegance is on the road to recovery, so that's good.

I'm on well water, if that maters... The RO/DI is plumbed into my water line after my water softener, and I have a basic mixing station that uses two 10g tanks to hold water. I have noticed that the first few cups of water out of the RO/DI have high TDS readings (~50), but it quickly drops back down to about 2ppm. Does anyone else have that problem?

Anyone have any other suggestions as to why I have a noticeable increase in nuisance algae in the 2 days following a water change? Nuisance algae is a non issue when I'm not doing frequent/regular water changes.

 

[Capt_Cully]

Do you have a flush kit? Perhaps flushing for 10 minutes or so, previous to collecting product, would do away with the initially high TDS water.

I started a thread about RO units a ways back. Link is in first page of my build thread. It is so informative, I'd dare say, youll find everything you need in it.

Let me know if you have trouble finding the link.

 

[block head]

i run the same rodi system. filters and resin are cheap. being a bit more aggressive with your maintence and dumping the first few minutes of production works well for me. ultra clean water is something easy ,and one of the few things i can control . euphilla are are fairly tolerant of less than ideal water. if your losing coral, i'd look at basic water chemistry before tds. i turkey baste my rock, and stir the water well prior to a WC . it does cause the nutrient level to spike a bit after a "reef snow"

 

[tmz]

tds post di resin should be 0.The resin will release those things that are loosely bound such as ammonia and silicate first. So 5 tds post di is likely much worse than 5 ppm tds post membrane.

How old is the membrane? What kind of rejection rate are you getting from it? That is , what is the difference in tds between the well water and the membrane output water?If the membrane is passing through thigh tds water it will use up the resin's adsorption capacity quickly.

 

[pascal32]

Second Tom. The di resin should always be zero coming out, even if you are passing high tds after your ro membrane. Are you using an in-line dual meter? If so put the in sensor before the di and the out afterwards.

Take a reading after 2-3 seconds, 2 minutes and 5 minutes.

Are you using color changing resin? If so you will see the color change to yellowish which means it needs to be replaced.

The filter guys are REALLY good about service. Give them a call!

 

[jacksonpt]

Do you have a flush kit? Perhaps flushing for 10 minutes or so, previous to collecting product, would do away with the initially high TDS water.

I don't. An occasional 10minute flush would be easy preventative maintenance. Might be worth a shot.

 

[jacksonpt]

i run the same rodi system. filters and resin are cheap. being a bit more aggressive with your maintence and dumping the first few minutes of production works well for me.

Hmmm... I can probably make that work with another valve and a T in the line.

euphilla are are fairly tolerant of less than ideal water. if your losing coral, i'd look at basic water chemistry before tds. i turkey baste my rock, and stir the water well prior to a WC . it does cause the nutrient level to spike a bit after a "reef snow"

Generally I agree with you, but the problem seems to be worse because of the less than perfect water coming in during a water change. Water params have never been perfect, but they've never been a problem either.

 

[jacksonpt]

How old is the membrane? What kind of rejection rate are you getting from it? That is , what is the difference in tds between the well water and the membrane output water?If the membrane is passing through thigh tds water it will use up the resin's adsorption capacity quickly.

membrane was replaced in the fall. I'm not at home right now, but IIRC TDS on the well water is 250ish. I would hope that it would last longer than 6 months, but...

 

[jacksonpt]

Second Tom. The di resin should always be zero coming out, even if you are passing high tds after your ro membrane. Are you using an in-line dual meter? If so put the in sensor before the di and the out afterwards.

Take a reading after 2-3 seconds, 2 minutes and 5 minutes.

Yes, currently I've got the in sensor before water hits the unit, so before any of the filters and the out sense after the DI canister. I'll try to take the readings tonight for some exact numbers.

Are you using color changing resin? If so you will see the color change to yellowish which means it needs to be replaced.

No, but I changed that about a month ago along with the other filter cartridges, so I would think it's still got some life.

The filter guys are REALLY good about service. Give them a call!

They definitely are, it's one of the big reasons I went with them. I've got an email out to them now, just waiting on a response.

 

[Buckeye Hydro]

I've been struggling with what I suspect to be bad RO/DI water issues basically since I set up my tank. I've got a 5 stage RO/DI system (Ocean Wave + 5 Stage 75gpd from the filter guys) with TDS meter. I replace the filters whenever I get a consistent TDS reading of 5 or higher.

Two thoughts for you:

First, and especially because you are on well water (which is not chlorinated), why are you using a system with two carbon stages? If you don't have a particular issue with your water quality that would be addressed by carbon (such as chloramines, which you don't) using two carbon filters is draining your wallet but not doing much useful for your water quality.

Second - No need to change all your filters when you notice your TDS climbing. This may help (from our FAQ's):
A good rule of thumb is to replace your sediment filter and carbon block after six months. A more precise way to maximize the usable life of these two filters is to use a pressure gauge to identify when pressure reaching the membrane starts to decline. This is your indication one or both of the filters is beginning to clog.

Also be cognizant of the chlorine capacity of the carbon block. A good 0.5 micron carbon block for example will remove 99% of chlorine from 20,000 gallons of tap water presented at 1 gpm. Some original equipment suppliers commonly provide carbon cartridges rated at 2,000 to 6,000 gallons.

Regarding your RO membrane and DI resin, use your TDS meter to measure, record, and track the TDS (expressed in parts per million) in three places:
1. Tap water
2. After the RO but before the DI
3. After the DI.

The TDS in your tap water will likely range from about 50 ppm to upwards of 1000 parts per million (ppm). Common readings are 100 to 400 ppm. So for sake of discussion, let's say your tap water reads 400 ppm. That means that for every million parts of water, you have 400 parts of dissolved solids. How do we go about getting that TDS reading down to somewhere near zero?

If you do some experimenting with your TDS meter, you'll note that your sediment filter and carbon block filter (collectively called “prefilters”) do very little to remove dissolved solids. So with your tap water at 400 ppm, you can measure the water at the “in” port on your RO housing and you'll see it is still approximately 400 ppm.

The RO membrane is really the workhorse of the system. It removes most of the TDS, some membranes to a greater extent than others. For instance, 100 gpd Filmtec membranes have a rejection rate of 90% (i.e., they reject 90% of the dissolved solids in feed water). So the purified water coming from your 100 gpd membrane would be about 40 ppm (a 90% reduction). Filmtec 75 gpd (and below) membranes produce less purified water (aka “permeate”), but have a higher rejection rate (96 to 98%). The life span of a RO membrane is dependent upon how much water you run through it, and how dirty the water is. Membranes can function well for a year, two years, or more. To test the membrane, measure the total dissolved solids (TDS) in the water coming in to the membrane, and in the purified water (permeate) produced by the membrane. Compare that to the membrane’s advertised rejection rate, and to the same reading you recorded when the membrane was new. Membranes also commonly produce less water as their function declines.

After the RO membrane, water will flow to your DI housing. DI resin in good condition will reduce the 40 ppm water down to 0 or 1 ppm. When the DI output starts creeping up from 0 or 1 ppm, you know that your resin needs to be replaced. Sometimes people complain that their DI resin didn't last very long. Often the culprit is a malfunctioning RO membrane sending the DI resin “dirty” water. This will exhaust the resin quicker than would otherwise have been the case. Sometimes the problem is poor quality resin – remember that all resins are not created equal.

Russ

 

[jacksonpt]

Wow, thanks Russ. Some great info there. Now I actually feel like I know how the system works and can better troubleshoot.

:thumbsup:

 

[jacksonpt]

Just an update...

I replaced all 3 filters and the DI resin, but not the RO membrane (changed that recently so it should be good... let tds readings tell me when to change it).

I'm now running a 5micron poly filter, then a 1micron poly, then a 5micron carbon block (may change this out at some point, but...), the RO membrane then the DI.

I also changed where I've got my tds sensors... one is between the RO and the DI, the other is after the DI.

I've been getting consistent readings of 1ppm at the first sensor, and 0ppm at the second.

I've done a couple of water changes and my hammer colony responded almost immediately (phew)... now I just need my elegance to be happy.

Thanks to everyone that offered suggestions, especially russ for the beginner's crash course to RO/DI.

I may pick up another TDS meter next time I order filters so I can check tds levels at the tap and immediately before the RO (should be the same, but I like seeing what's goings on as water works through the filter system).

one last question... what exactly does an auto shut off do? I rarely.turn the supply to the filter off, I use float valves to control production. I've read that auto shut offs are required when using float valves, but I've never read why.

 

[shroutk3]

The auto shut off make it so that the waste water isn't still being produced when the float closes. Without auto shut off, the float will close and waste water will still be produced continuously- This is less that ideal as it's a huge waste of water.

 

[Buckeye Hydro]

shroutk is right on the money.

Russ

 

[jacksonpt]

Thanks everyone. Looks like I'm good to go for a while.