Nitrates in RO/DI water

[mfuchs]

I am having a problem with high nitrates in my RO/DI water. My tanks all have nitrate levels approching 100mg/l!!! I tested my RO/DI water and it shows 12mg/l.

I figured that maybe it was time to change out the DI filter so I ordered a new one. I installed it and started making new water. I tested that water and it also tested 12mg/l. So now I am thinking that maybe my source water is really high in Nitrates. So I tested it, and it also tested at 12mg/l!! So I guess my DI filter is not removing any NO3.

I always thought that the DI filter removed Nitrate as well as Nitrite and Ammonia and other compounds? Or is my problem with the RO membrane?

My ammonia and Nitrite levels are both zero.

Also, I figured that my NO3 is high because all my water changes have not been removing NO3, but adding it. Is my line of reasoning correct? Or should I be looking for another culprit for the High Nitrate?

Thanks in advance for your help.

 

[Leaf]

What test kit are you using?

Approximately how old is the test kit?

 

[mfuchs]

I am using Tetra Nitrate test kit. I am not sure how old it is, but I would guess not older than a year. Probably around 8 - 10 months. I was thinking about getting a new test kit, but I also have other signs - such as hair algae that I can't get rid of and the fact that I have also lost two Yellow tangs - that were otherwise healthy.

What test kit do you recommend?

 

[cmor1701d]

Look elsewhere for your high nitrate problem. If you remove 10 gallons of water at 100ppm of nitrate and add 10 gallons of 12ppm water, you have diluted the total nitrates. If this was a 50% water change you would have almost halved your nitrate level. If this was a 150 gallon tank, a 10 gallon change would not make much of a difference.

Do you have a tds meter?
What is the tds of the tap water?, RO water? and RODI water?
You are right in that the DI should remove any remaining nitrates.

I also believe your test kit is wrong. I use the Salifert kit as I found it the easiest to read (for me). The SeaChem kit is also pretty good.

Nitrates approaching 100ppm are bad for fish. You really want to keep it under 40 for a FO or FOWLR tank.

You can try a couple of 50% water changes to bring the level down.

You need to determne where your nitrates are coming from!

What are you feeding the tank, how much and how often?
Do you have a protein skimmer?
A sump?
Are you using a wet/dry or cannister filter or HOB filter? How often are you cleaning the filters?
What is the tank substrate? CC (crushed coral) can collect a lot of detritus which will decompose to nitrate.

 

[Kurt_Nelson]

Looking at the Tetra nitrate kit, it looks like "12" is the very first color step above zero... correct? If so, then you could just be getting a false positive on your RO/DI water. I'd get a different test kit that can measure in smaller increments. Salifert nitrate kits can measure down to 0.1ppm.

But a reading of 100 for your main tank is a different story! You probably do have an issue there, and as cmor mentioned it probably has nothing to do with your source water. A little more detail on the tank and maintenance/feeding habits might shed some more light.

 

[Leaf]

But a reading of 100 for your main tank is a different story! You probably do have an issue there, and as cmor mentioned it probably has nothing to do with your source water. A little more detail on the tank and maintenance/feeding habits might shed some more light.

Any fish deaths or cleaning crew die off(s) lately?

 

[mfuchs]

Here is a little more of a twist for you all, I have two friends of mind that use my RO/DI water for their Freshwater tanks and one of them also has high Nitrates (the other I have not tested, but her fish just got ick). This is what led me to believe it was my water.

But as for my tank:
180gals with about 150 to 200lbs or more live rock. I have a protein skimmer and a wet/dry with a 40gal sump. The sump does not have bioballs in it because of the amount of LR I have in the tank. I mainly use it for my Protein Skimmer, macro filtering and my Phos-ban reactor.

As for changing out or cleaning my filters - I admit that I could do a better job at it....

I do have CC but it is finely crushed (if that makes a difference). I also have some sea weed type planets.

I also am having a problem with hair algae and have lost two yellow tangs in the last couple of weeks.

As for feeding, I feed marine flake food and I would like to believe I do not feed them much. I only feed them once a day and do so sparingly. I always preach to my friends to not overfeed their fish.

My tds meter says that the tap water is 140 and my RODI water is 3.

I will go and purchase a new test kit (I think I will try the Salifert) and see what I get.

As for my friends tanks - one has ick and the other tank that I have confirmed has high Nitrate, has lost fish lately in it and is having an algea bloom too.

Hope this helps..... Thanks again.

 

[lando]

GHA?...PO4 levels? High nitrates can certainly feed unwanted algae, but IME PO4 is much more of an issue. First things first...verify your source water NO3 level with a different test kit and go from there. I also suggest testing for PO4 in your tank and source water...it is more likely the source of your GHA.

Replacing the DI membrane is only part of the solution. I would also suggest replacing the DI resin and any carbon and sediment filters as well.

Not sure what caused the death of your yellow tangs. More info will be needed to help with that issue. Age and size of the tank, acclimation process for the tangs, how long they were in the tank, any signs of disease or parasitic infestation, diet, eating etc.

 

[Kurt_Nelson]

If your final RO/DI water has a TDS of 3, then I'll put money on the fact that the test kit is giving you bogus results. Nitrates of 12ppm and TDS of 3 just don't seem to go together - not that they're remotely related. But a TDS of 3 is pretty darn close to pure water. I'm guessing you tested your friend's nitrates with the same test kit you're using?

Your DI resin is probably shot and should be replaced. The DI should bring that number down to 0.

 

[mfuchs]

I also suggest testing for PO4 in your tank and source water...it is more likely the source of your GHA.

PO4 is 0, I tested that initially with two different test kits(I guess I should have done the same with NO3). I was also under the impression that PO4 is the main culprit for GHA. I just learned that NH3 contributes to it too.

Replacing the DI membrane is only part of the solution. I would also suggest replacing the DI resin and any carbon and sediment filters as well.

I replaced the DI Resin just before my initial post, I have not replaced the RO membrane, I don't think that is the culprit. Tuesday I ordered a new carbon and sediment filter just to be sure.

Not sure what caused the death of your yellow tangs. More info will be needed to help with that issue. Age and size of the tank, acclimation process for the tangs, how long they were in the tank, any signs of disease or parasitic infestation, diet, eating etc.

Tank size is 180 gals. The tank has been setup and running for 4.5 years. I have had the tangs for about 8-10 months. I figured they died due to the 100mg/l NO3. They did not have any visible signs of disease. They always ate, but like most tangs, they always look skinny.

 

[mfuchs]

I'm guessing you tested your friend's nitrates with the same test kit you're using?

You got it! I though I put that in my post, but I omitted it...sorry. I will pick up a test kit today and retest...

Your DI resin is probably shot and should be replaced. The DI should bring that number down to 0.

I replaced the DI resin on Monday. The funny thing is that ever since I got the RO/DI, the TDS reading has always been 3, or at least it has never been 0. I have had the RO/DI for about 2 years now.

 

[Kurt_Nelson]

The DI resin should strip it down to 0. While 3 really isn't a big deal, it sounds like maybe the TDS meter is a little out of calibration since you just replaced the DI resin.

Dumb question... you DO have the RO tubes hooked up correctly... right? Just thought I'd ask because every once in a while there's a person that has the waste line going into their DI stage and is draining out the good water. That gives you pure water for a real short time, but really blows through DI resin fast!

 

[cmor1701d]

How are you testing the tds? I normally start with a new plastic cup and fill that with just enough RODI water to get a reading on the meter. Last time I used a cup that looked new but was not fresh out of the bag. TDS was 25. I rinsed it with my RODI water and tested it again. It was 5. I rinsed again and the third test was 0. Just throwing that out as a possible cause for getting 3 tds on your RODI test.

Your tap water at 140 tds is very good. Mine ranges from 185 - 215.

 

[mfuchs]

Dumb question... you DO have the RO tubes hooked up correctly... right?

No, I do know that they are connected correctly. Mainly because the RODI water that comes from the resin is a slow drip, while the waste water is more of a steady stream(but not a lot of water - just noticable more than the other.) I also just connected a RO flush kit two nights ago and confirmed it was connected correctly. But it never hurts to ask or double check because we all make mistakes.

How are you testing the tds?

My RO/DI has a in-line meter. It has a sensor at the input (source) line before it enters the prefilter and another one at the line from the DI canister to my reservoir. There is a unit that I turn on and then select a switch that looks at the in and out sensors and displays the results.

 

[cmor1701d]

Have you contacted the manufacturer of the RODI unit to ask about the reading. Do you have the instruction manual, and if so does it tell you how to calibrate the meter?