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Discussion Starter · #1 ·
Hi,

I am building arduino based ph controller but I have problems getting stable readings. When I tested ph in plastic jar readings ware stable, but when placed in aquarium ph was all over.

After some google consulting I realized that the problem might be ground loop. I measured voltage between aquarium water and ground and it was 2.2V ac, current was 0 mA ...uh

I then changed my power supply for arduino from switching to transformer to achieve galvanic isolation and that worked ...until lights came on. I have Juwel T5HO 2x54W.

Should I ground aquarium water? Any other idea?

Thanks,
Gorazd
 

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I'm unfamiliar with setup but u can put an amp probe around a filter water line and see if ur geting amps. If so then ur wall socket may not be grounded well. It sounds strange I know.
 

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Discussion Starter · #3 ·
I measured current and it is 0.

2 prong equipment (not grounded)
- juwel powerhead
- 150W heater
- juwel T5HO 2*54W light fixture

grounded
- external filter with UV-C (internally only UV-C electronics is grounded)

The only problem are lights which have no contact with water. The question is:

- do lights induce voltage into water?
or
- lights electronic ballast emits EMI back to power outlet?

Thanks, Gorazd
 

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Have you tried disconnecting each item like litghts, filter, etc. to find which might be giving trouble? Ballasts are EMI suspects.
 

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Discussion Starter · #5 ·
I tried grounding aquarium water but it does not help. The only piece of equpment that influences ph readings are lights. When turned off ph is stable at 7.18, when on ph jumps from 6 to 8.
 

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Children Boogie
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After looking at schematics on your link I had an idea. I connected copper wire from aquarium water to ph interface gnd and it worked.

There are still some ripples around 0.05 ph but that can be fixed by averaging readings.

I am using this http:// http://www.sparkyswidgets.com/product/miniph/

Thanks to all
Gorazd
Glad it worked but that solution sounds weird, perhaps from a not well thought out design on the device. Well at least it's only $18.
 
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