Adjusting things 250 km from the aquarium is normally not so good because it is impossible to check things on site. As you can see in lat post . I succeeded to dial it in rather good but.....
I lowered the dose Sunday at noon. The reason for the decreasing ORP readings could be low flow or dirty redox probe. I was home late Sunday evening and let it be for the day. Yesterday I decide to clean the pump and the probe and do some samplings below the DSB. Some result come up that I probably have to rethink some conclusions. The situation get worse - the plenum start to be more or less anaerobic - at least my probe report that.
After cleaning I decide to do some changes in the automation. Before I had use static parameters for the pump and dose of ethanol. I decided to keep the static for the dose but change the speed of the pump to dos 0.1 ml/minute. It means that it will take 2 minutes to dose 0.2 ml every 15 minutes (96 dose/24 hours) The software (and hardware) of GHL´s doser 2.x allow these settings with the latest FW. I had notice that with every dose - ORP decline. Therefore I programming the water pump to run when I dose and for 10 sec more. Using PL command delay off. However - I dose 2 minutes every 15 minutes - ORP can decline the other 13 minutes. If that happens - I have set the pump to react on decreasing ORP outside dose time. I set the redox control to nominal value 240 mV as a start, hysteresis 15 mV (blue). Controller on pulse variable and length of 5 min as max and fixed pause of 30 sec (black) This means that the controller is on if the real reading is below the nominal value and if it is far away from the nominal value it will run for max 5 minutes. Wait 30 seconds and if it still away from the nominal value it will run again. If it closer to the nominal value it will run shorter time and wait once again 30 sec. If it reach the nominal value during the cycle - it stops. This is a perfect controlling feature that allow you to have a much softer adjusting compared with the normal on/off controlling. The time I have set - you need to adapt to your system and how fast the system respond.
I have now to combine the two conditions for the pump to run - condition 1 - run when ethanol is dosed and condition 2 - run when the ORP is below the nominal value. It is done with a PL command as well.
PL 30 (pump runs when dosing ethanol)
PL 31 Combination with redox controller and the command OR
All of this has nor result in a rather smoth regulation of the flow and ORP
I also did an analyse of NH3/NH4, NO3m NO2 and PO4 both in the water below the DSB and in the DT. Remember - there was rather anaerobic compartment below the DSB a day before these analyses - hence probably the shocking NO2 concentration below the DSB. The diagram have also been adjuste - it was wrong figures for NO2 in the plenum before - forgotten a 0 on the wrong place
NH3/NH4 - still much of it (if not all) disappear when the water pass the DSB (reversed flow) Phosphate decrease. NO3 higher below the DSB than in the display tank for the first time and NO2 rather high in the plenum.
If the system works as it should and that I can control the ORP around 240 mV - I will take new measurements next week.
PO4 and NO3 in display tank during may 2024
Sincerely Lasse
