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Seachem Prime and false positives

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  • Seachem Prime and false positives

    Recently I became aware of the potential for Seachem Prime to cause different water tests to return false positives, in particular with the Nutrafin liquid ammonia tests (freshwater in my case). I did get quite a shock when I tested a bucket of water I'd treated with Prime and that was to be added during a water change - 0.6ppm and more of ammonia. I do tend to leave my water 24 hours before I add it to the tank (even though I've been told I don't need to), and I'd got the false positive 2 hours after treating - 24 hours later I no longer got one. I've experienced the same with my aquarium water itself after dosing with Prime, so it has quite the knack of throwing Nutrafin liquid ammonia tests off...fortunately I'd first experienced it with the replacement water, so I had a suspicion that I wasn't looking at rising ammonia levels.

    I don't seem to have had the same difficulty with API liquid ammonia test, but I have read that the reading needs to be taken immediately because the Prime will break down and cause a false positive. I'm assuming this means that after letting the colour develop (5 minutes), it's best to compare against the colour card as soon as possible, and that as time progresses the test will be fouled?

    What other false positives might Prime cause with tests? Since it detoxifies nitrites at sufficient dosage, would it be safe to assume that as I approach that dosage (anything from a lower 2x to the required 5x and greater), a water test could also start to give me a false positive of nitrites? I'm talking Nutrafin liquid nitrite test here - I own both Nutrafin and API test kits, I like to cover all bases and if I find one of the tests isn't reliable, I have a fall-back.

  • #2
    Re: Seachem Prime and false positives

    I just thought of another good question to ask: when taking the potential for false positives into account, how long after dosing with Prime is it wise to conduct any particular water test that might suffer from a false positive? I've read Prime remains active between 24-48 hours, so is it correct to assume it can affect tests up to that 48 hour mark?


    • #3
      Re: Seachem Prime and false positives

      Anyone able to answer my questions?


      • #4
        Re: Seachem Prime and false positives

        I apologize for the delay. I wanted to take the time to reply in detail.

        From our FAQ about Prime:

        "Q:I tested my tap water after using Prime and came up with an ammonia reading. Is this because of chloramine? Could you explain how this works in removing chloramine?

        "A: Prime works by removing chlorine from the water and then binds with ammonia until it can be consumed by your biological filtration (chloramine minus chlorine = ammonia). The bond is not reversible and ammonia is still available for your bacteria to consume. Prime will not halt your cycling process.
        "I am going to assume that you were using a liquid based reagent test kit (Nessler based, silica). Any type of reducing agent or ammonia binder (dechlorinators, etc) will give you a false positive. You can avoid this by using our Multitest Ammonia kit (not affected by reducing agents) or you can wait to test, Prime dissipates from your system within 24 hours."

        When we talk about false positives, there are two things that can occur. With some test kits, (particularly those using using Nessler reagents) you may see an off chart color.

        With most kits which test for total ammonia, (like the API test kit) you will get an accurate total ammonia reading but not an accurate free (toxic) ammonia reading. What this means is that it will not tell you is the ammonia has be detoxified. Prime works to detoxify ammonia by binding the ammonia and holding it in a non-toxic state for about 48 hours. Total ammonia test kits break this bond and convert it to free ammonia, so you will still get a reading if you test it. Our MultiTest: Ammonia kit can test for both free ammonia and total ammonia. Also our Ammonia Alert only reacts to free ammonia, so it is great to use in a new tank or an overstocked tank where the potential for an ammonia spike is high.

        The instructions that you have read about reading the API ammonia test immediately after the color develops (after five minutes for this test) is based on the fact that Prime (like all dechlorinators) is a reducing reagent. If the reductive potential of the Prime in the water sample hasn't been used up, it can begin breaking down the color indicator in the test kit, causing the color to fade. The longer the Prime has been in your system, the less likely you are to see any affect. Usually any reductive potential is used up within 24 hours but it might be much sooner depending on what is in your water. Any ammonia, nitrite, or nitrate which has been detoxified will usually stay bound for about 48 hours.


        • #5
          Re: Seachem Prime and false positives

          Thank you for the reply.

          What I was seeing with the liquid Nutrafin (Nessler-based) ammonia test was zero ammonia readings (or virtually zero - I swear I always see even a smidgen of colour development, hence why I also use API just in case, to double-check) prior to dosing the aquarium itself with Prime, then a few hours later 0.6+ ammonia readings, and then about 11 hours after dosing with Prime it's back to normal.

          This was repeatable: the first time I noticed it I tested about 5 hours after dosing with Prime and then 11 hours after dosing things were back to normal (tested at 11:15pm and 7:30am, time of dosing ~6:15pm); the second time the first test prior to dosing was ~6:20pm and everything was fine, then the second test after dosing was ~8:15pm - two hours later - and I was getting 0.6+ in ammonia readings again. This is all bearing in mind I dose my tap water with Prime and hold it back for 24 hours prior to adding it to my tank, and my tests on the water I was holding back in that instance resulted in definite 0.6+ readings after 2 hours, but back to zero after 24. In the second experiment I hadn't even carried out a water change that evening.

          As for the nitrites issue, either it's because my test was borked somehow, I've been cleaning my filter too thoroughly and I did have a nitrite spike, or possibly in sufficient concentration perhaps Prime causes a false positive with the liquid Nutrafin nitrite test (we're talking very faint colour here, having to rely on the ring of water at the top of the sample for the most colour development).


          • #6
            Re: Seachem Prime and false positives

            With a Nessler-based ammonia test kit like the Nutrafin kit, you will get a true false-positive. Usually the color will look a little "off", but you can get color even when their is no ammonia in the water.

            With the nitrite test kit, it is possible the Prime could be reducing some of the nitrate to the nitrite form and this is what you are seeing when you test for it. Prime does detoxify nitrite so any slight reading you may see wouldn't represent a danger to your aquarium inhabitants.

            For more information about test kits and how they work, we have an article about test kits in the SeaGrams section under the Library tab: .