A larger sump seems like it would account for both issues.
If you don't want to scrap your current sump, maybe you could add an additional sump tank connected with a bridge siphon.
Thanks Guys I was hopping there was an easier way because my sump tank is buried in the ground below one of the grow beds..... But you are all correct, a bigger sump would solve the problems.
Hmmm, I'll bet you could drill a few very small holes in one of the standpipes. That way if your pump runs dry, there will still be some water coming into the system to trigger the other siphon.
Or you could just go with a timer based system and an indexing valve. You'd only be filling one growbed at a time then.
I've used an indexing valve for three years and like it - have never used a siphon or sump.
With a 500 gallon tank you could easily have a six bed system, using a six way indexing valve. The valves come four way also.
My pump runs for 8 minutes every two hours so each of six beds is flooded only 2 times per day. I also have an air lift pump running continuously to one grow bed. Things seem to be working well, other than some recent pump trouble.
Yeah, I'm with George (and Alex) on that one...in my 8 IBC grow bed + DWC system, I've been using an indexing valve for over 3 years as well...and in a few other 4 grow bed systems. It allows you to use a much smaller sump than you could have without the valve.
Some folks bemoan the fact that turning your pump on and off so frequently shortens the life of the pump, but my magnetic drive pump has been running (with the indexing valve and a repeat cycle timer) for well over 3 years without fail (so far)...and no siphons to deal with
Dennis, you really need to take a pic or draw something up as your system is not conventional. The beds normally drain back to the sump individually and not in series as you describe. My buried sump is 275g and it only varies about a foot running 5 ibc GBs. Running them in series you are asking for trouble.