sharky03us

I have an Oakton TDS tester; the tester 1.

My question is this. Will the Oakton tester (or any tester) give an accurate ppm reading of Fox Farms--Grow Big, Big Bloom, and Tiger Bloom mixed in combination?

Here's a quote from Oakton's tech tips:
"It is absolutely necessary to use a calibration solution similar in dissolved solids content to the solution to be tested in order to get acceptable accuracy."

I calibrate using General Hydroponics Standard Reference Solution@25c.

So, are organic-based ferts similar in dissolved solids content to the calibration solution?

cheech wizard

A lot of organic nutes consist of undigested organic compounds vs salts. Normally a TDS meter is going to read low compared to chemical ferts of comparable nutrient content. However, even w/ chemical ferts, the TDS reading doesn't actually tell you what the concentration of nutes might be, it just gives you a conductivity reading that should be roughly proportional to the available nutrient concentration. You want to establish a baseline first, then adjust based on plant behavior vs your readings. Assuming you already have some experience w/ your nutes of choice, you can mix like you normally would, take a reading and use that reading as a baseline. Alternately, you can start w/ the manufacturers recommendations, take a reading and that becomes your baseline. Additionally, if possible, find someone using the same nutes and use their info as a baseline.

Accuracy is less a factor than repeatability. However, the meter has to be calibrated to a standard.

I could be wrong, but I believe all this is saying is that in order to get the best accuracy, calibrate to a standard that has a similar conductivity to your mixed nutes.