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To calibrate TDS meter you need to have 000 TDS RO water. If you have no 000 TDS water then the easiest way is to replace resign in filter (you need good quality resign for instance Triton Di). If you replaced resign in your filter then swich on the whole Reverse Osmosis filter and wait arround 10 minutes. Then click “calibrate button” in Smart reef.
Regards
Reef Factory Team