Anyone test newly made salt water at this time of year?

[DKoKoMan]

I mixed up some salt (RC) and will test tomorrow. Funny thing is I do WC biweekly and my nutrients have stayed the same for the longest time Nitrates 2-5ppm (Salifert) and Phosphates 0.02ppm (Hanna Phosphate checker). I tested today like every Sunday and noticed an increase in my PO4 at 0.10ppm.

I recently bought 4 new pails of RC on Black Friday... and I have done two WC’s using one of the new pails... I’m hoping it’s not a source of phosphate as mentioned above.