Yeah, running at higher PH levels isnt the automatic death sentence some people would have you believe. I figure the roots in my system have spent more time above 6 than below since early in the grow - when the tank first got infected. The main issue I have seen is burning from over feeding, but there have also been some signs of Mg def - but not real bad. Purple stems mostly.
I can drain the accumulator tank bck into the rez manually, and have done it quite often. I have a T and a valve in the system between the pressure pump and the accumulator tank that I can use to drain the accumulator back into the rez. I have been doing that when ever I change the EC - especially lowering it - or when the PH has gotten way out of hand, etc. I also did it when adding chlorine or copper - to get the treated water into the entire system at the same strength.
The only down side to doing that is that my solenoid type pressure pump is noisy. Plus, when I drain the accumulator tank all the way down, it takes long enough to re-fill it that the pump gets kind of warm. Its still within spec as far as max temp, but it gets hot enough to make me want to be careful. So, when I do a 100% drain, I do the re-fill in two stages allowing the pump to cool in between. This is the main reason I want to change over to the diaphragm type pump when I can afford it.
In order to automate this you would need to start the drain cycle right before the pump turned on and run it long enough to drain a significant amount of the tank, but not long enough to drain it completely. I think that would require a second pressure sensor. I dont know how you would adjust a timer on the fly to run at the proper time. Well, I guess you could just run it long enough to do a partial drain.
Other wise, if the drain cycle happens when the pump is running, you would just be re-circulating water that was fresh from the rez rather than water from the tank. The accumulator tanks only have a single in/out tap, so you can only fill it OR drain it - not both at the same time.
Im thinking this issue can be handled three different ways.
it could be automated with another pressure sensor/arduino setup, but thats down the road. Its not going to be a simple programming thing either. There are different degrees of hysteresis in different parts of the system to deal with. The rez will react pretty fast, but the accumulator tank will be a good bit slower, and the nozzles slower yet.
In the mean time, I can just keep doing it manually as needed. Rather than dumping large portions of the tank back into the rez, I think I can come up with a schedule to raise the PH in the rez so that the PH at the nozzles climbs at a reasonable rate, but I will have to play with that some more.
As a data point - I raised the PH in the rez last night at around 9PM. Its now 8AM and the tank PH is flickering between 5.6 and 5.7, so its gone up just a bit in the last 12 hours. The PH at the nozzles is still a solid 5.6. The pressure pump ran one time between when I did the change and now - about 3 am. It ran again just after I took samples this morning.
Thats another detail to track. If I take samples right after the pump has run, there will be fresh water from the rez in the lines and in the tank that will read the same as the rez until it has time to equalize with the water thats already in there.
Thats good news! Did you use any chlorine or anything to kill the crap or just flush? I have no clue if your gunk is the same as mine, so you may not need to kill anything.
That gets pretty exciting doesnt it I launched a nozzle across the room one time and had a heck of a time finding it!.
Is that 2.2 gallons the nominal volume or the actual amount it can hold? Atomizer said that most tanks only hold about 3/4 of the nominal volume. My tank is listed at a 5 gallon, but the spec sheet show an "acceptance volume" of 3.8 gallons. By my calcs its actually closer to 3.7 gallons of real usable volume.
If that 2.2 is nominal volume, then your tank probably actually holds closer to 2.2 x 0.75 = 1.65 gallons. If you are running 80 psi to 120 psi, then that works out to about .49 gallons per re-fill. Thats almost exactly what mine is at the moment. The big difference is yours will cycle much more often than mine does. Your PH changes should propagate through your system much faster than mine.
I added a section to the spread sheet that does the tank math. Insert your actual tank volume, cut in and cut off pressure settings. It will calculate the volume of air in the tank and how much volume you actually get out between those two pressures.
change .PDF to .xlsx
flowrate.pdf (14.2 KB)