Since tap water Params often fluctuate the TDS could have dropped in your tap and your top offs have been lowering it.
My tap is usually in the 45-50 PPM range. Though I don't think doing top-offs with tap would lower the TDS.
can i ask why you have blue velvets in with rili? as for tds if u use powder foods that might do it.
I wanted to see if I could get more blue midsections in my red rilis. So far it's been going alright. I've gotten a mix of red rilis, blue rilis, some blue velvets, and oddly colored rilis in the progeny (some greys and a rili with orange spots). Though most of my reds looks a bit bluer in the midsection. I don't selectively cull though since catching them in a heavily planted tank is near impossible. So I'm satisfied with what I end up with.
I don't use powdered foods and I don't understand how using them would lower the TDS over time. If anything, they would raise the TDS.
bioassimilation from your plants. if you have any fast growers (floaters in particular, like hornwort, or duckweed) they will be sucking fertz out of the water, lowering your TDS.
Most likely. My floater mix would cover the entire top of the tank if the bubbles from the sponge filter didn't keep them engulfing that tank corner.
Anyways, I found the calibration fluid. However it's at 1382 PPM, too high to calibrate with since you're supposed to calibrate your TDS meters with an NaCl solution that has a TDS in the same range you're normally used to seeing. I'll probably go to the local hydroponics center on my day off and see if they have any 326 PPM calibration solution.
Here's a pic of the tank:
It's supposed to be a lot darker but the phone on my camera automatically bumped up the brightness.
And here's the mass of floaters.
It's a mix of giant duckweed, frogbit, DWL, and a bit of hygroryza that's slowly being smothered. I'll probably replace most of the floaters with some antler fern I got locally from another member. Also, Don't mind the aphids. They're pretty much impossible to get rid of.