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Measuring pH of really clean water is tricky.
If you want to check your RO equipment function, you should use an inexpensive TDS meter instead.
 

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Correct - RO water when exposed to air absorbs carbon dioxide which lowers the pH. With no buffering the pH drops to about 5.0-5.5. Color indicators are acceptable for measuring pH of low TDS waters (compared to pH probes - they don't work correctly in RO water), but pH alone doesn't tell you if the RO system is working properly.
 

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Discussion Starter · #4 ·
Correct - RO water when exposed to air absorbs carbon dioxide which lowers the pH. With no buffering the pH drops to about 5.0-5.5. Color indicators are acceptable for measuring pH of low TDS waters (compared to pH probes - they don't work correctly in RO water), but pH alone doesn't tell you if the RO system is working properly.
Alright thank you for your help, i bought a TDS meter.
 
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