Which tests do you perform with your DR890 and specific method?
I ask only because my DR900 has like 4 different methods for phosphate, a few for nitrite, nitrate and ammonia. Also, procedures for nitrate from hach website also say if testing sea water need to be recalibrated to be accurate. Did you have to do this with you DR890?
These are the testing methods I use:
Ammonia: Salicylate Method.
Phosphorus: PhosVer 3 (Ascorbic Acid) Method
Nitrate: Cadmium-Reduction Method. This sensitive to chloride concentrations and results in seawater are low. At one time, I had spiked Hach's nitrate standard with salt and recorded absorption to find multiplier. Unfortunately, I have lost that file. I'll order that standard next time and repeat the procedure. Without correction, the nitrate in my tank is presently at 0.5 mg/L.
Color, True and Apparent: Requires filtration of sample to determine True Color.
Copper: CuVer Method.
Iron, Ferrous: 1,10 Phenanthroline Method.
Iron, Total. FerroVer Method: Total Iron minus Ferrous Iron = Ferric Iron.
Nitrite: Diazotization Method.
Fluoride: SPADNS Method.
I expect to receive a DRB 200 block heater today and plan to order TNT Total Nitrogen (requires sample dilution) and Total/Acid Hydrolyzable Phosphorus. These numbers can be used to determine organic/inorganic species.
For Alkalinity and Total Sequential Hardness (Calcium/Magnesium): Digital Titrator using sulfuric acid and EDTA titrants, respectively.
ORP, Dissolved Oxygen, and pH: Intellical probe and appropriate sensors coupled with a Hach HQ40d datalogger.
I have also tested spiked samples for Zinc.
These are testing I do off the top of my head.
The DR 890 is a fine instrument and has given me years of service. Eventually, I'll upgrade to a newer instrument capable of measuring TNT Plus reagents.