Yes, you can trust your meter readings.
Most EC-meters need little calibration. Once every 6 months is fine, and you can make the liquid yourself if you have access to a lab scale. It's just some salt and distilled water.

Forgot to mention . . . Yes, you must subtract the tapwater reading. That bit of hardness in the water(Ca + Mg) becomes part of your nutrient.

Great. Thanks for the help!

Where did you get your EC meter from?

I bought this one. It was about $55 after s+h. It's quite cheap relative to others, and comes with batteries, but it's not clear how I'll be able to change them out when they die, since it seems to be a solid unit. Here's a picture.

Oh well, I'm sure it will last a few years anyway.

A different brand but it looks very similar to my pH meter. Probably made by the same manufacturer and re-branded by others.

I believe you should be able to pull the top (where the on/off switch is) out to access the batteries.

Bill

greystoke,

what's the math for making your own?What is the water/salt ratio?
Thanks,
mudcat

Your meter is fine. Your under 10 on distilled. Then your good. You might be off 15 points 20 at most. Who cares if your accuracy is off a little your fine.

mudcat65 wrote:
what's the math for making your own?What is the water/salt ratio?

I've got 577mg NaCl(dry kitchen salt) per litre of distilled water gives you 2000µS.

"I've got 577mg NaCl(dry kitchen salt) per litre of distilled water gives you 2000µS"

So, .5*577mg=1000?1.5*577mg=3000?

I'm not sure I understand that formula. However, . . . I DID make a mistake. It's 925mg/L for 2000µS. NOT 577.

There's NO fixed relation between ppm and µS. All depends on the type of salt in solution. For kitchen salt its about 50%.

I have a truncheon meter and love it. does not require calibration. its water proof. and it doubles as a stir stick.

Yes I got the truncheon meter becuase it doesn't need calibration - one less thing to bother with.