What is Reddit's opinion of GuDoQi PH Meter, TDS Meter Combo, Pool Water Test Kit, PH Tester Digital, PPM Meter, 0.01 Resolution TDS PH EC Temperature 4 in 1 Set for Drinking Water, Hydroponics, RO System, Aquarium, Swimming?

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Amazon!!!
Normalmente lo usan para albercas y acuarios.

PPM (Partes por millon) también se utiliza para medir la presencia de ciertos gases en el aire.
Sobre los filtros, no se si te refieras a la capacidad del filtro para atrapar partículas de cierto tamaño (micras).

If you're not "vaporizing" the water, the white powder wont be the issue. You'll definitely want to balance the PH of your water if you're not already. It's super easy to do. Buy a PH meter and some PH Up & Down on Amazon and use it to balance the PH for the type of soil you're using every time you water - usually between 6.0-7.0. If you're not balancing PH, chances are you're going to run into some serious issues at some point.

Edit: Also, de chlorinate your water if you're pulling directly from the tap. Let it sit for 24 hours before using to water the plants - it's as simple as that.

Agua antes del filtro, agua después del filtro paso 2, agua del mini split y agua bonafont.
Nada mas que regrese el agua y hago la prueba.
Esto es lo que uso para revisar el agua en el acuario:
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