Phosphate in my NSW ?

[mike550]

I've started to keep some new saltwater in storage (cool and covered) and just noticed that the phosphates in the container are around 0.012. I'm going to test it again in about a week. But I thought that NSW shouldn't have any phosphates in it?

If it matters, I'm storing in a Brute container and using TM Pro for the salt. Starting with RODI water with 0 TDS.

Thanks in advance.

 

[AutumnReefs]

What phosphate test did you use. I HIGHLY doubt the test is accurate down to that level.

 

[mike550]

What phosphate test did you use. I HIGHLY doubt the test is accurate down to that level.

I use the Hanna Ultra Low Range Phosphorous (HI 736) which has the following specfications:

• Range: 0 to 200 ppb
• Resolution: 1 ppb
• Accuracy: ±5 ppb ±5% of reading

 

[Randy Holmes-Farley]

Too low to be any issue, and it is not unusual to get a little coming through an RO/DI:

Aquarium Chemistry: Phosphate And Math: Yes You Need To Understand Both

Foods are by far the most important source of phosphate in most aquariums. In considering whether sources of phosphate other than foods are important, one must carefully look to the actual amounts involved to determine whether other sources are even worth trying to minimize.

reefs.com

Comparison of Food Sources of Phosphate to Other Sources
What about other sources of phosphate, like the “crappy” RO/DI water containing 0.05 ppm phosphate? A similar analysis will show it equally unimportant relative to foods.

Let’s assume that the aquarist in question adds 1% of the total tank volume each day with RO/DI to replace evaporation. Simple math shows that the 0.05 ppm in the RO/DI becomes 0.0005 ppm added each day to the phosphate concentration in the aquarium. That dilution step is critical, taking a scary number like 0.05 ppm down to an almost meaningless 0.0005 ppm daily addition. Since that 0.0005 ppm is 40-600 times lower than the amount added each day in foods (Table 4), it does not seem worthy of the angst many aquarists put on such measurements. That said, tap water could have as much as 5 ppm phosphate, and that value could then become a dominating source of phosphate and would be quite problematic. Purifying tap water is important for this and many other reasons.