You have enough parts for a basic three-level water indicator using three BC547 transistors, three LEDs, three 220 Ω LED resistors, and three 10 kΩ base resistors; the fourth transistor can be a spare. The tank’s 500-liter capacity does not determine the circuit—probe heights set the indicated levels, and I need your power-supply voltage before confirming resistor values; use only an isolated, low-voltage DC supply, never mains-connected probes.

I haven’t created a schematic or changed your empty project yet. Execution stopped because your ACUs ran out.