Can i use this in the sump of my aquarium rack, by just mounting the sensors in the water in the sump? ie not inline in an ro/hma system?

There are 2 problems. The sensors are calibrated to be used as advised and in open water they will give much higher readings as well as having the uncertainty of their durability. The latter issue is not a short term problem as they are just 2 probes on the end of a pair of wires. It all depends on what you want to achieve.

Tds meter should 2 digit result. should this be 3 digit? e.g 000ppm ??

Its a 3 digit readout on an instrument with 2% accuracy. Do not confuse accuracy and precision. Accuracy is how close to the correct result is it? 2% is 2 parts in 100, so some of second digit and all the third digit are wasted. It can determine only 50 TDS steps. Precision is what does it display? The display has 1000 steps, so its very precise. That is 0.1% precision.

I have an RO unit with a post filter to reinstate minerals, should this be installed before the post filter? Or will readings be affected?

I have mine after the water comes out of to unit I think if you put post filter all minerals could be filtered out

Trying to recalibrate while disconnected from RO unit but the in and out probes give different readings, why?

The probes have to be in the pipe to read. They will not give a “correct” reading if pulled out of and say placed in a cup. You would need to use the T connectors and loop a piece of pipe around

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HM Digital DM-1 in-Line Dual TDS Monitor, 0-9990 ppm Range, +/- 2% Readout Accuracy

HM Digital DM-1 in-Line Dual TDS Monitor, 0-9990 ppm Range, +/- 2% Readout Accuracy

Product ID: 48028052

Details

Brand
HM Digital
Item dimensions L x W x H
48 x 20 x 76
Item weight
45 g
Material
Plastic
Number of items
1

💧0-9990 ppm TDS range

🔋Auto-off power saving

⚙️+/- 2% readout accuracy

¥9304

Duties & taxes included

In stock

Sold byAmazon JapanDelivered byDesertcartCustomer service byDesertcartReturns14 days · 30 with PRO

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Description

💧 Know your water, own your purity.

DUAL INLINE PRECISION - Simultaneously monitor tap and purified water TDS for real-time filtration insights.
SMART POWER MANAGEMENT - Auto-off after 10 minutes conserves battery life, so your monitor is ready when you are.
EFFORTLESS INSTALLATION - Quick-connect fittings and compact design make setup seamless—get pure water faster.
MICROPROCESSOR ACCURACY - Advanced tech ensures reliable readings within ±2%, empowering confident water quality decisions.
ULTRA WIDE DETECTION RANGE - Measures TDS from 0 to 9990 ppm, covering all water qualities with ease.

The HM Digital DM-1 is a compact, dual inline TDS monitor designed for precise water quality tracking in filtration systems. With a broad 0-9990 ppm range and ±2% accuracy, it provides real-time comparison of tap and purified water TDS levels. Featuring quick installation, advanced microprocessor technology, and an auto-off function for battery conservation, it’s ideal for professionals seeking reliable, on-demand water purity insights.

Specifications

ASIN	B001EHAZGW
Best Sellers Rank	15,067 in Business, Industry & Science ( See Top 100 in Business, Industry & Science ) 67 in Liquid Analysis Instrumentation 175 in Lab Meters
Brand	HM Digital
Country Of Origin	China
Customer Reviews	4.7 4.7 out of 5 stars (2,704)
Global Trade Identification Number	00891144000052
Included Components	Bag
Item Dimensions	48 x 20 x 76 millimetres
Item Weight	45 g
Manufacturer	HM Digital, Inc.
Manufacturer Part Number	DM-1
Material	Plastic
Model Number	716186
Number of Items	1
Set Name	Dual
UPC	733169337600 891144000052 885169394012 885156810310
Unit Count	1.0 count

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