Week 4 was defined by the discovery and correction of a significant salt and nutrient buildup in the medium. On Day 21 (Jan 20), runoff opened at 2100 PPM — well above safe range — triggering an emergency flush. Feed input came in at 418 PPM at pH 6.99, and multiple plain water rinses at pH 5.8 were run through the medium until runoff dropped to 1180 PPM at pH 5.87, EC 2370 µS/cm, salt 0.11%. Medium was flushed down approximately 920 PPM in a single session. No further watering for 24 hours following the flush to allow the root zone to stabilize. Environment ran well overall — temperatures holding 76–78°F lights on and ~70°F lights off, humidity steady at 68–70% with brief transient dips when the humidifier tank ran empty. VPD tracking ~0.9–1.0 kPa throughout the week. PPFD running 380–420 µmol/m²/s. CO2 ambient with no supplementation. Day 25 (Jan 24) feed came in at 642 PPM at pH 5.91 — notably the water temperature was very cold at 4.7–6.0°C, well below the ideal 20–22°C range. Cold water can slow nutrient uptake and stress roots. Worth monitoring in future sessions to ensure water is allowed to reach room temperature before feeding. No runoff recorded this session. By end of week, runoff had settled to 1440 PPM at pH 5.8–5.9 — trending in the right direction. Feeding plan reset going into Week 5: ½ gallon at 600–700 PPM, ¼–⅓ strength veg nutrients only, no boosters, pH 5.9 target with 10–15% runoff. Goal was a gentle nutrient reintroduction to signal roots to resume uptake without risking a salt rebound. The Sundae Thumper continued developing steadily through the stress of the flush week.​​​​​​​​​​​​​​​​