04 Jan 2019
Manual pH Testing on a Shrimp Farm – The Dangers of Relying on Them
Written by Zach Stein

pH Drops and Strips on a Shrimp Farm – The Dangers of Relying on Them

pH is a critical parameter to track on a shrimp farm, and yet the vast majority of farms still conduct their daily pH testing by hand using drop or strip tests. While relatively inexpensive, these tests have major problems that all farmers should be aware of before relying on them.

 

Color is Hard to Read Accurately

The human eye is an amazing thing, but we all have slightly different ones. If the light is different, or someone is slightly colorblind, the readings they take with a handheld test can be wildly off. We’ve seen managers correct their employees in the field after they were off by over 1.5. This is a huge difference!

It is very hard to trust those water quality readings when the margin for error with color read by the human eye is so high.

 

pH is Logarithmic, not Linear

Should someone be able to read color reliably and consistently the next problem occurs when color falls in between one of the set points on the scale. It’s halfway between bright green and dark green. The problem here is that pH is not a linear scale, it is actually logarithmic, so just assuming that something is halfway between means that margin of error is again very large as the water could actually be 10’s to 100’s of times more or less acidic or basic than estimated.

 

The Tests Aren’t Actually that Cheap

We calculated that running a series of drop-based tests (more than just pH) costs a little over a $1/day per pond. This is not a negligible amount, especially for a system that is dubiously trustworthy at best. Osmobot, our continuous monitor, costs a little over $1/day as well and uses a camera and computer to analyze colorimetric dyes for pH and ammonia with much better results than the human eye.

 

Conclusion

If you are still using drop or strip pH tests for your shrimp farm, consider a change, or at the very least, consider updating your practices to protect against inaccurate readings and the logarithmic scale.

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