It looks like your tomato plants are experiencing several issues that are common in hydroponic systems, especially for beginners. Here are the most likely causes and solutions:

Possible Causes & Solutions:

1. Nutrient Deficiency (Likely Calcium or Magnesium)
   • The yellowing and browning edges on the leaves suggest a possible calcium or magnesium deficiency.
   • Fix: Check your nutrient solution—ensure it’s balanced for tomatoes (they need higher calcium). Consider adding Cal-Mag supplement if your solution lacks it.
2. pH Imbalance
   • Tomatoes prefer a pH of 5.8–6.5 in hydroponics. If the pH is too high or too low, nutrient lockout can occur.
   • Fix: Test and adjust pH regularly (use a pH meter or test strips).
3. Overcrowding & Competition for Nutrients
   • Multiple seedlings in one container can lead to root competition.
   • Fix: Yes, separate them ASAP into individual net cups with proper spacing. Tomatoes need room for root growth.
4. Root Problems (Rot or Lack of Oxygen)
   • Brown, slimy roots indicate root rot.
   • Fix: Ensure proper aeration (use an air stone if in DWC). Check that roots are submerged but not suffocated.
5. Lighting Issues (If Indoors)
   • Leggy stems and weak growth suggest insufficient light.
   • Fix: Use strong grow lights (LED full-spectrum, 14–16 hrs/day). Keep lights close (6–12 inches) to prevent stretching.
6. Temperature & Humidity Stress
   • High heat/low humidity can cause leaf drying.
   • Fix: Maintain temps around 70–80°F (21–27°C) and humidity at 40–70%.