TDS Calibration Solution

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Captive Purity

Calibration Fluid for TDS meter with automatic temperature compensation.

**Variations of this product can be found in many online stores. The version we carry is of the highest quality. Although this item is eligible for price matching under our Low Price Guarantee, please be certain the product you want to price match is the same make and model.

Manufacturer Info

Captive Purity manufactures water filtration and water testing supplies for marine and reef aquaria. The brand is best known for their high-quality line of reverse osmosis filter systems and accessories. Captive Purity also produces refractometers for testing salinity, portable pen-sized meters for testing pH as well as replacement filter media for their RO and RO/DI filter systems.

Pam from


Experience Level: Intermediate

Not many alternatives

I have a handheld TDS meter that I use to monitor the water quality of my reverse-osmosis unit. It is supposed to be calibrated with 443 ppm (not the 800 ppm of this pack) and can't handle anything over 999 ppm. Traditional calibration fluid for hydroponic meters is way above 1,000 so it can't be used. There simply aren't a lot of options out there. The good side is that it is easy to tear off the top of the packet and stick your meter inside, and you can be confident it hasn't evaporated in storage. The bad side is that it is still too high for ideal calibration. I'm still uncertain how accurate my two meters are. Despite being sold as factory calibrated they read quite differently - one significantly too high and the other too low. I guess I'll have to go to a medical supply store to see if I can get normal saline there and use that to calibrate my meters.

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