What should my pH be in a saltwater tank?

The pH or a marine aquarium should be in the range of 8.1-8.4. The pH of the ocean is approximately 8.3 and if you can pH up to 8.3 and hold it there, great, but most salt mixes mix to about pH 8.1. What’s important with pH is that it doesn’t fluctuate on a daily basis and is stable. A reef tank with a permanent pH of 8 is better than one that goes up to 8.4 and down to 8 in a day. Radical changes in pH are dangerous to marine organisms, so should be avoided. 

How do I test pH in a marine aquarium? 

Test pH with a liquid pH test kit or an electronic pH tester. This should be accompanied by other test kits and if you have a reef tank you should also test for KH, Calcium, Magnesium, Nitrate and Phosphate. pH is important but the value that will drop the quickest is KH, and should be buffered on a daily basis. 

How can I raise pH in a saltwater tank?

If your pH is below 8, the easiest way to raise it is with a water change. Use a good quality refractometer to test the salinity of the water as if the water isn’t salty enough it will likely not have a high enough pH either.

If you want to take pH above 8.1 to 8.4, it’s a bit more technical. Firstly you can put a CO2 scrubber on the inlet of your protein skimmer. Secondly, you can dose something called Kalkwasser, a highly caustic solution which raises pH. It’s not recommended for beginners, however. An easier way to do it is to add a Marine Buffer. This can be added to the tank regularly and will raise pH to 8.3. It will also have an effect on KH, so monitor both closely when using it. 

Is my pH too high?

pH shouldn’t be above 8.4 in a reef tank, so if it is try a different test kit just to confirm, first of all. If the pH is above 8.4 stop adding any pH buffers and it should come down naturally. If you want a more instant result do a partial water change but remember not to bring pH down to quickly over 24 hours. 

Is my pH too low?

If your pH is below 7.9 its too low. Conduct several partial water changes, buffer RO water before adding salt, and consider adding a pH buffer.   

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Jeremy Gay is an author and freelance aquatic specialist. A former editor of Practical Fishkeeping magazine, he offers a wealth of experience on all things aquarium and pond.


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