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Water testing - when and what I measure

  • water-testing

Water testing is a necessity for a happy reef.

Water tests are performed often. Specific key areas may be checked or tested daily or every few days, but the full battery of tests are done once or twice a month. When those are completed, that is when I update my spreadsheet and post it on the site.

For more information about testing and maintaining stable water parameters, refer to this article:

Below are the basic parameters within acceptable range limits, but a tighter swing within the high and low range is best.  For example, if pH measures 8.1 to 8.3 daily, that would be better than 7.9 to 8.4 daily.  The more consistent with limited variation, the better.

Test Type Recommended Parameters matching Natural Sea Water (NSW)
Salinity 1.026 sg - a calibrated refractometer is the best tool to measure salinity. A hydrometer will measure specific gravity, while a refractometer will show parts per million. 35ppt is the target measurement that is closely equal to 1.026 sg.
pH 7.9 to 8.3 - this varies daily in a tank; measure with a Pinpoint Meter or controller rather than a test kit.
Temperature 78° F to 84° F - average reef temperature tends to be 81° F; try to keep within a 1.5° to 2° swing at the most.
Alkalinity 8 to 11 dKH -or-  2.86 to 3.89 meq/L
Calcium 390 to 450 ppm
Magnesium 1350 - 1400 ppm (or 3x Calcium levels)
Phosphate .03 ppm - leading cause of nuisance algae in your tank: click for article
Ammonia 0 - anything higher is toxic
Nitrite 0 - anything higher is toxic
Nitrate 10 ppm or less - huge water changes bring down nitrates: click for article


Here are some example measurements over time, many years ago.  I probably should do some type of online record once more seeing how it's 2017... I'm still testing water often, but not adding them to the website like I used to years ago. Here's this week's latest measurements at least:

May 7, 2017
Alkalinity 9 dKH - Elos 
Calcium 375 ppm - Elos
Magnesium 1350 ppm - Elos
Phosphate .25 ppm - Elos
Nitrate <2 ppm - Elos
pH 8.35 - Apex pH probe
Temp 78.8° F - Apex temp probe
ORP 295 - Apex ORP probe
Salinity 1.024 sg - Milwaukee Digital Refractometer

EDIT: November 2017: I just started tracking my parameters with the new iOS ReefTrace App. 

In February 2011, my new 400g reef was started. Readings are taken at various times, and are documented here to allow you to see how the parameters vary over time.



Readings from my 280g reef were taken at various times, and are documented here to allow you to see how the parameters vary over time. This aquarium ran for nearly six years, but in early July 2010 it sprung a leak. Any measurements thereafter were taken from the livestock vats while the new system was being built from the ground up.




2007 - 2006

2005 - 2004


* Both reef tanks were upgraded to a 280g during this year.



Blank entries were not taken for whatever reason. Certain tests are ignored, such as Ammonia because they typically result in 0.

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400 Gallon