Backyard Aquaponics
A place to discuss aquaponics

Ive been playing with my multimeter to see if I can measure nutrient levels (or anything) by checking resistance while adding my first doses of fish emulsion.

I was hoping I could get a nutrient free base level and then I could tell when the nutrient had been consumed before adding any more (its a fresh system with no fish)

My readings start high 120.0 (200k ohms) and drop steadily from the moment I start to measure eg. down to 68.3 after 15 minutes.

does anyone know enough about such things that they might be able to tell me if I've made a tiny capacitor out of a AP system?

It just occurred to me that if i switch to voltmeter i should see some voltage...and i get .96 volts and falling fast

I think i just made a rechargeable battery!

If this is the first step in the creation of some new blue barrel scoria megga battery ive just invented I craig kirby donate it freely to the world under the GPL

Is there anything aquaponics cant do????

-craig

Are we cycled yet? Are we cycled yet? Are we cycled yet?

Probably earth leakage from your pump Dont stick your tongue in there.

Actually I checked it with and with out the pump

But it also made me think so I put a safety switch on the plug (some people in this beer drinking land of ours wire an outside plug without going through the safety switch (for the beer fridge) so the freezer defrost cycle doesn't trip it)

So boys and girls...

--- Never trust an aussie outside power point ---

-craig

Its actually very difficult to measure EC of a hydroponic solution with a multi meter. the current flowing across the terminals is DC and it will plate the dissolved salts from the solution onto one prong of the multi meter and increase its resistance so the reading drops with time. EC meters use an alternating current to lower the problem and you have to clean the terminals fairly frequently - if you wipe the multi meter probes well the reading should return to the initial value. You have to keep the probes a fixed distance apart too for the readings to mean anything.
Don't know why you would see a voltage reading if both probes are fairly close together in the water - I suspect it probably has more to do with the internal circuit in the multimeter than with the solution. any solution of salts will form a battery of sorts with dis-similar anode and cathode materials (like the carbon rod and the zinc casing of a standard torch battery) but with the probes both of the same material I wouldn't expect to see any voltage.

EC readings have very little meaning in aquaponics solutions anyway - they only measure dissolved salts and the nutrients from the fish are not in the form of salts like a hydroponic solution. also if you run sea salt in the system the reading will be off the scale as far as hydroponic solutions go.

probes were set at opposing corners of the tank to try to maintain a known distance apart.

the voltage test is repeatable. always shows voltage that falls off.

might have to check my multimeter



cool thanks for your reply.

I was never sure what I would be measuring anyway, but thought it might tell me something

Hopefully I'm getting some kind of test tomorrow.

-craig

your neighbours are going to think you're a nutter

doesn't sound like a capacitor, resistance should have gone from low to high

_I_ think I'm a nutter but my neighbors are half a km away so know nothing

-craig