I'm very glad to have things back to "normal". Having the fish in the sump required me to run one grow bed at a time, and I was constantly worried about the fish stressing out in the smaller space and with the drastically changing water level.
Pictures of the fixed tank and swirl filter below. Also, I decided to go with a much simpler and less costly sump container. It is now a much bigger hole lined with pond plastic liner. The first picture shows the sump. It only looks dirty because the liner is clear and the dirt you see is the earth underneath the plastic. You can tell it's crystal clear by how visible the pumps are underneath the water. This plastic is used in commercial tilapia farming, is UV-resistant, and is supposed to last 5 years. I think I'll get a little more out of it in my semi-shaded and small-scale operation.
New Sump. The Fish Tank outer wall is to the left. Don't let muddy floor fool you - it's transparent lining over a hole in the earth.
New Swirl Filter. Water is gravity fed from the fish tank the via the 3" overflow pipe which discharges water about 2/3 of the way down the tank in counterclockwise direction. It exits through a 2-1/2 " inch "funnel" near the tope of the barrel which is connected to a 1" drain pipe that send the water to the sump. This type of filter works in two ways: first, by discharging the water below and making it travel up, that provides time for solids to fall out of suspension; secondly, the swirl effect caused by the vortex in the middle causes water on the outer perimeter to spin much more slowly than water in the middle, also providing time for solids to fall out. Once in the sump, water is pumped both back into the fish tank and to the grow beds.
The barrel is a "blue barrel" of about 200 liters.
The run from the fish tank is long and awkward, but that's what the space I have allows. I've wound up changing much of the original plans, but I think it will ultimately make for a better system.
The plants are doing much better now that the PH levels are under control. They appear to be growing more quickly and are definitely greener and more healthy-looking. I got a handle on the situation starting last week, with the careful addition of phosphoric acid. It still has not stabilized, but I believe it is on its way. Washout from the gravel is completely ruled out as affecting the PH. A sample of the gravel soaked in water yielded stable PH after a small addition of phosphoric acid, and held over a week.
Below are the latest pictures of the plants. The squash plant died back when I transplanted the plants from the bath tub to the large grow bed, and my jalapenio plant died this week. That one had already been dying in a dirt pot but revived in the AP system - until this week. Now it really looks like it's kicked the bucket.
I am not dissapointed by the plant results. AP system take a while to stabilize anyway, during which time plant growth is weak. That, plus the PH problems in the beginning and the transplant of the bath tub plants did not lead me to have evry high hopes to begin with, so I am pleasantly surprised.
My next plan is to set up a floating raft system as part of this system. There is plenty of space for it and it is reported to be the best way of producing lettuce. An additional filter to take finer solids out before sending the water through a floating raft system will be needed.
The bath tub bed went back into operation this week. I could only run two beds with the temporary sump/fish tank. Lettuce and spinache (barely visible here) were planted. Can't wait to see what they look like next week!