Reef fact? Filter water to test PO4 when using lanathum?

csb123 · Jul 14, 2019

I was getting erratic PO4 readings and it may be due to the use of lanathum chloride. When LaCl is added, it precipitates with phosphate and carbonate. The precipitate for a very fine sediment. I do filter my water with floss, but this sediment may be getting through.

I’ve only done it a couple of times, but the results are interesting. Using the Hanna ULR phosphorus tester, I tested my water straight out of the tank, and also after running it through a COFFEE FILTER.

The results are: (conversion PO4= (test result x 3.066)/1000)

7/11/19 unfiltered 0.046 filtered 0.028
7/14/19 unfiltered o.o37 filtered o.o12

So, the filtered water shows a significantly lower result.

Since this testing uses up reagent and is time consuming, please post your results if you try this.

Thank you,
Sean

Randy Holmes-Farley · Jul 14, 2019

Any particulates will scatter light and could lead to a false high reading with a spectrometer unless the water is filtered, or the test uses a blank using that water before the reagents are added.

csb123 · Jul 14, 2019

Thanks for weighing in, Randy!

The checker tests the water before and after the reagent is added.

Is there a chance that the checker is reading total phosphorus, including suspended lanathum phosphate?

When you’re trying to maintain tight control of PO4 the difference in readings is significant.