All the variables (and doubt) of testing water params

[bzb]

I did the unthinkable - I left my new tank alone for almost a week! Granted, I was halfway across the country, so that might have been a big contributor.

When I got back, I noticed new bright green algae growth on a couple rocks, and the diatoms seem to be fading a bit (or the mimic tang is just that good at controlling it). When I left, there was a tiny bit of ammonia and nitrite still detectable, and nitrates were undetectable. So I ran tests using an API kit on Sunday:

Ammonia: undetectable
Nitrite: <0.25ppm (ever so slight purple tinge)
Nitrate: 10-20ppm

So naturally, I think time for a water change, and go ahead and clean the equipment. I cleaned out the skimmer cup (very dry foam made for about a 1/8" of almost black buildup) and cleaned the pumps with RODI. I did not clean the sump - there's still a good bit of detritus on the bottom of each chamber, but I didn't want to disturb any of it in case I've got pods starting colonies. Using IO Reef Crystals, changed 8 gallons total, or ~12% water change.

This morning I test the water and I get:

Ammonia: undetectable
Nitrite: still slightly purple tinge <0.25ppm
Nitrate: undetectable

I ran the Nitrate test twice because I am so confused. The math doesn't work out right, obviously. The skimmer isn't producing any foam in the cup yet. Heaters are on the InkBird, running Tunze ATO. Everything in the tank is still happy (as far as I can tell).

I know not to obsess over these things, but what in the heckadoodle? Either it's time for a better kit than this API stuff, or maybe I did it wrong Sunday night? Any suggestions here?

 

[FutureInterest]

Sounds like you have a new tank since nitrite is still visible. Having the nitrites/nitrates skip around is plenty normal at this stage. Nitrates don't soak into the substrate or rocks so a 12% water change should just reduce your nitrates by 12%. I like the api test kits for just quick and fast testing but sometimes they can give odd results depending on how long you wait before each step or an accidental drop or bubble showing up in the drop. I'm nearby so if you need someone to verify your tests you are welcome to bring some water by.

Overall, I wouldn't stress about the sudden change in nitrates. Most likely that first test was just off if the two tests afterwards coincided.

 

[bzb]

Appreciate the feedback and the offer!

Yep, not quite a month old, cycled with ammonia hydroxide and Fritz Zyme 9, then added a piece of live rock from Nemo, then three total fish a few days apart from each other (along with a GSP frag). It does seem to be jumping around, so I just need to be patient still, I'm sure. Thankfully, no serious spikes have happened, which I'm pretty certain is from the Fritz product.