PH reading low

PostPosted: Wed Sep 12, 2012 8:44 am
I have been out of the country for the past month and have used the portal to monitor the tank. I noticed around three weeks ago the the PH was dropping every day. I got my son to go over and check the PH using an API kit and the PH was within the normal range for the tank.

Over the next three weeks it dropped to 5.3. I have now taken a look at the problem, and have found that if I remove the ATO connection from ATO1 then the reading goes up to 6.13, but no higher.

I have cleaned the probe without effect, but I cannot get any calibration fluid until the weekend, I am not sure it is a calibration issue anyway.

The questions are, is it an interference or connection issue with the ATO circuit, or is my probe faulty?

And how do I resolve it?

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Joined: Fri Mar 18, 2011 6:47 pm
PostPosted: Wed Sep 12, 2012 8:55 am
It could be stray voltage from the float switch.
It definitely has some interference by what you just described.
So, the first thing would be to replace the float switch.
It could also be stray voltage from one of your pumps.
What ph value do you get when you place the probe in a cup of tank water?
Roberto.
PostPosted: Wed Sep 12, 2012 6:25 pm
I disconnected the extension lead to the probe and plugged it direct into the RA head unit. Placed the probe in a glass of tank water and after one hour the reading was 6.4.

It looks like the probe to me.
PostPosted: Wed Sep 12, 2012 8:13 pm
The reading is the same in tap water.

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Joined: Fri Mar 18, 2011 6:47 pm
PostPosted: Wed Sep 12, 2012 8:56 pm
What numbers do you get when you load this code:
Code: Select all
#include <Salinity.h>
#include <ReefAngel_Features.h>
#include <Globals.h>
#include <RA_Wifi.h>
#include <Wire.h>
#include <OneWire.h>
#include <Time.h>
#include <DS1307RTC.h>
#include <InternalEEPROM.h>
#include <RA_NokiaLCD.h>
#include <RA_ATO.h>
#include <RA_Joystick.h>
#include <LED.h>
#include <RA_TempSensor.h>
#include <Relay.h>
#include <RA_PWM.h>
#include <Timer.h>
#include <Memory.h>
#include <InternalEEPROM.h>
#include <RA_Colors.h>
#include <RA_CustomColors.h>
#include <RF.h>
#include <IO.h>
#include <PH.h>
#include <ORP.h>
#include <AI.h>
#include <ReefAngel.h>

void setup()
{
  ReefAngel.Init(); 
}

void loop()
{
  ReefAngel.LCD.DrawText(0,255,10,10,ReefAngel.PHMin);
  ReefAngel.LCD.DrawText(0,255,10,20,ReefAngel.PHMax);
  ReefAngel.LCD.DrawText(0,255,10,30,ReefAngel.Params.PH);
  ReefAngel.LCD.DrawText(0,255,10,40,analogRead(PHPin));
  ReefAngel.Refresh();
}
Roberto.
PostPosted: Thu Sep 13, 2012 8:08 am
Roberto here are the results from your test code.

Probe in cup of tank water

540
830
628
470

Probe in tank

540
830
648
490

Probe in cop of RODI water

548
830
695
539

PH tested at 8.1 using API kit

Posts: 12482
Joined: Fri Mar 18, 2011 6:47 pm
PostPosted: Thu Sep 13, 2012 9:03 am
Looks like the probe is no good anymore.
You can't really measure pH on RODI, both tap and tank look too low.
Did you leave in vinegar for a couple days when you said you cleaned??
Roberto.
PostPosted: Thu Sep 13, 2012 11:43 am
No I did not do a long soak, but I will give it a try now, and give it a good two days.

If that does not work I will order a new one, there are a few other bits I want as well.

Many thanks
PostPosted: Mon Oct 15, 2012 3:15 pm
I replaced the probe and after several attempts to get it calibrated it worked OK for about three weeks.

It has once again started to gibe bad readings. My test shows a PH of 8.2 and the new probe 6.3.

I am beginning to thing it is due to stray voltages from the ATO switches. So I have just order the new water level expansion unit to see if that helps.

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