Nitrates disapeared - but for no reason

HI folks.

10 Gal has completed its cycle and has been established for several days now. For the last few days we've had NH3 and NO2 at zero, while NO3 has been steadily climbing through 10, and up to 15ppm as of yesterday.

We've added no live plants or new fish. In fact we've made no changes to the tank. We were planning to toss in a plant and a cory tomorrow.

Today, Nitrates tested off the scale low... after adding the the re-agent the test tube water instantly went almost clear and stayed that way for the required 5 minute wait. I repeated the test 2ce more with the same results. Yes, I shake the living daylights out of the re-agent for at least 30 seconds before using it.

The only other thing of note was a scare from one of the neon tetras yesterday... shortly after feeding we noticed it swimming oddly (nose down, unable to maintain depth without constant effort), it's belly was bloated to one side, but no raised scales. We were debating setting up an ad hoc hospital tank but decided to wait a bit and see how things went. Within the hour the neon started to show improvement with no bloating and better swimming. By the end of the second hour it was happily baiting the danios.

I don't know if the tetra's issues and the disappearing nitrates are related or if the timing was coincidence.

 

I'm not sure how this would happen (swI'm bladder disease?), but it sounds like the tetra had some sort of bubble in its body.

As far as the Nitrates dropping, I'm not sure. Are you absolutely positive that nobody involved added a Nitrate absorber to the filter? Was a new water conditioner used? I know you said no changes were made, but I'm just checking.

 

Sirdarksol,
Absolutely no changes. Only one other things occurs to me -- our little 7 year old nephew paid us a visit the other day and we were amusing him with the fish tank -- help with testing, toss a couple flakes in, that sort of thing.

At one point he stuck one of his finger into the water to see if a fish liked the taste of him. I noticed then that the little nipper had half the garden under his fingernails. Maybe he introduced something? If so, I want to know what it was and I'll try to market it.

 

Unlikely that the garden would affect things, but possible. (I'm a sci-fi/fantasy nut, so the improbable yet still possible always comes to mind. Besides, it's not terribly likely that nitrates would just drop off the scales. In this case, I think we've got to follow Sherlock Holmes' advice). He could have introduced something that eats nitrates. Presuming that this extremely long shot was the case, however, whatever it is probably can't actually live in water, and it would end up further polluting the water, so keep watching your numbers.

Does it look like an algae bloom is gearing up? Did the water get clear very quickly? (I've noticed this immediately before I get a bloom. The algae sucks all of the cloudy stuff out of the water before it gets populous enough to see)

These two things are the only ideas I can come up with. Keep bringing info as you figure things out. Someone's bound to either have or stumble over the right answer eventually.

 

One thing we didn't consider -- contaminated test tube maybe, but I did the test 3 times. The lady of the house came home to my perplexed look and did a 4rth test. Guess what -- it came up pretty much on the nail with what we expected in the first place.

Weird. Now I have to live with her derisive giggles and haughty airs of superiority.

All back to normal.