I cant tell much from the chart, I just don't know how exactly it is you keep records. By looking at it, I see two pH levels for each day so I can't tell what is going on there. Also I have no idea what the values under fertilizer refer to, but anyway.
A 50 gallon reservoir is huge for two small plants, but not a problem. If you are maintaining the pH between 5.5-6.5 you should be fine there. If the
nutrient temp is kept between 65F and 75F continuously, you should be OK there also. Though 75F is at the upper edge, and I would prefer it to be lower. I don't use PPM/TDS/EC meters myself, and I'm not real familiar with maxigrow
nutrients. But if I'm not mistaken the directions recommend 1 tsp per gallon for the maxigrow. With plants that small you could probably do fine on 1/2 to 1/3 the recommended mix.
What is the air temp?
What is the watering cycles?
How high does the water level get with each cycle?
Is it humid, Is there good air flow?
Do the leaves wet?
Do the plants get plenty of good light?
Do you see any pests or bugs on them?
Are the plants cool weather or warm weather variety's?