N03 in RO Water

[Branch]

Last week I renewed the membrane, pre-filter and carbon filter on my DD RO system as it was overdue and showing nitrates of 5mg/l. Following the change I tested the water only to discover a reading of 10 mg/l. I rechecked that the membrane was inserted fully, they can sometimes be difficult to fit tightly, which it was and also tested my source water which had a nitrate level of circa 35 - 40mg/l so it isn't a case of very bad tap water. I'm waiting for my TDS meter as I lent it to someone however does anybody have any thoughts as to why this is happening? It's frustrating doing water changes knowing that the water I'm putting back in is already near the maximum I want in my tank. Before anyone refers to the PH issue for false readings, in the past the Salifert tests have always shown zero N03.

[Willie]

I recommend you take a water sample to a local fish store to double check your results. The comment is not meant to doubt your competency, but standard practice for all laboratories is to double check their own results against another standard.

I point this out because the EPA standard for maximum allowable nitrate is 20 mg/L (20 ppm). Levels higher than this can be toxic to infants, so probably not great for adults either. The fact that you're getting high results out of the tap water and positive results coming out of R/O suggest something is askew. In a properly functioning R/O system, there should never be more than trace nitrate readings. Also, a TDS reading is not going impact nitrate levels.

[LizStreithorst]

Did you backflush the membrane before you checked the product sample? I always do but I'm not sure whether or not it matters.

[Branch]

I recommend you take a water sample to a local fish store to double check your results. The comment is not meant to doubt your competency, but standard practice for all laboratories is to double check their own results against another standard.

I point this out because the EPA standard for maximum allowable nitrate is 20 mg/L (20 ppm). Levels higher than this can be toxic to infants, so probably not great for adults either. The fact that you're getting high results out of the tap water and positive results coming out of R/O suggest something is askew. In a properly functioning R/O system, there should never be more than trace nitrate readings. Also, a TDS reading is not going impact nitrate levels.

Thanks. Unfortunately my results are backed up by the water company's own results, we have high nitrates where we live I've seen then up as high as 90mg/l. In the past this RO system has only shown trace N03 hence my query. The TDS meter was not in respect of the N03 but to test the water coming out.

[Branch]

Please explain? I've never back flushed the membrane it's new and was installed properly last week.

[LizStreithorst]

My unit has a backflush valve on it. You should backflush 5 minutes either before or after each use and I imagine after installing a new membrane. I don't know how you would backflush without that valve.

[tomte25]

@Branch Backflushing will allow your RO membrane to last longer. If your unit didn’t come with a back flush valve, you likely can add one (I did with mine).

[Branch]

@Branch Backflushing will allow your RO membrane to last longer. If your unit didn’t come with a back flush valve, you likely can add one (I did with mine).

Thank you. This afternoon I tagged on a triple stage HMA filter to my RO system that I'd had lying around for years and the outflow water is now 0 nitrates as opposed to 10mg/l before?

[LizStreithorst]

Excellent. It doesn't matter how you solve a problem as long as you get it solved.

[Charlyc11]

@Branch Backflushing will allow your RO membrane to last longer. If your unit didn’t come with a back flush valve, you likely can add one (I did with mine).

I don't know if my iSpring 300 GPD has one the manual does not say unless it does it automatically. I saw that Amazon sells them for $8.99 cheap enough.

[dspeers]

Not that this addresses the RO issues but the EPA standard for NO3 is 10 ppm or 10 mg/L measured in nitrate nitrogen. The conversion factor to measured nitrate is 44.268 ppm or mg/L. Most home assays for nitrate measure nitrate not nitrate nitrogen. If your water company is really repetitively at 90 either nitrate or nitrate nitrogen then it is in violation and I assume subject to severe civilian liability due to adverse medical consequences. If you are reporting what is in your well water then you also want to cut down your intake. Although the greatest risk is to infants < 6 months, even adults can have adverse reactions, occasionally life threatening.

Most recommendations for discus tanks are also in nitrate units, far less than can be safely tolerated by humans.

[Branch]

Yep mine has a backflush valve, have never used it as it's rare my system is off for more than 2 days plus my ratio is no less than 4.1 so it's arguable whether it's needed apart from flushing toxins off new membrane?

Water in tank now 10mg/l so things seem to be heading in the right direction.