Sorry to hear of more issues.
So far your pics do not give me an accurate idea of your whole system setup.
A) - System Layout / Specs
Layout of growbed looks circular.
What is the Depth ?
Where does water go in ?
Where does it drain out ?
Where is the fish tank ?
Shape & Depth ?
Where does water drain in from growbed ?
Where does it pumped out from ? (location of pump inside the tank)
What water volume does it pump per hour ?
What are your pumping cycles ?
Do you pump at night also ? .... OR
Only pump cycles at day time ?
What grade is that sand ? .... OR ...
Is it a fine 2-3mm crushed gravel ?
Your excel file data suggests yet more questions need to be asked.
The lack of daily test results makes it more difficult to track, trace, identify and resolve issues as they arise and recede.
B) - Water Testing
What testing methods/kits do you use ? (Liquid, digital, powder, tablet - What Brand/s ?)
How old are they ?
Can you do all tests at same time and post a picture of all the results ?
C) - "OXY - YES"
Please explain this notation in your data file.
Is this additional O2 from compressed air cyclinder ? ... OR
Is it from an Air Pump ? - OR - Blower ?
Is "OXY" on any type of daily cycles ? ... OR
"OXY" is on 24hrs day ?
D) - Importance of Test Results
Have I mentioned the high importance of accurate, daily records ?
Oww... Yes, I have.
It is almost impossible to accurately determine where your system sits within all the potential Nitrogen Cycle scenario's.
I note you have 3 systems, but data for only 1 ?
You should test each system every day - test everything - and record the data separately.
3 individual systems = 3 individual sets of water test records.
E) - Importance of Test Results
You current data points out an interesting piece of information and raises another question.
Are you doing anything at all in the slightest bit different between the 3 systems ?
System 1 mortality is much lower in this round of issues.
It is still my view that you have rampant bacterial issues on several fronts.
1) Your Nitrogen Cycle (bacteria) is not / has not cycled correctly
2) If the current fish mortality look the same as previous - ie: bleeding into fins, redness of tissue
I would recommend that you consider;
Doing all tests again - on all tanks - record each tank separately - and post pics & data
Reduce the feeding portion a little (for the short term)
Do a 30% water change on each tank.
Consider adding another 1ppm of salt to each tank.
Post a couple pics of any future mortality.