Hermann tortoise lethargy after wrong UVB bulb

A coil UVB bulb on a Hermann tortoise for six months is a really common and genuinely damaging mistake — those compact coil bulbs don't produce the UVB output or spread that Mediterranean tortoises need, and the result is almost always UVB deprivation, suppressed vitamin D3 synthesis, and the lethargy you're seeing. Getting heating and UV lighting right is the single most important factor in tortoise health — metabolic bone disease, poor appetite, and immune suppression all trace back here. To point you toward the right fix: what size is the enclosure, how old and how big is the tortoise, and is the coil bulb the only UV source they've had, or have they had any outdoor time?

That picture makes complete sense given what he's been through. A 16cm adult Hermann needs strong, consistent UVB across the whole basking zone — the kind that only a proper linear T5 HO tube delivers. Coil bulbs max out around UVI 1–2 even directly underneath them, and the output drops to almost nothing at the distances tortoises actually bask at. Your tortoise has likely been vitamin D3 deficient for months. Before I give you the specific product, one question: do you currently have a separate basking bulb providing a hotspot of around 35°C, or is the coil doing all the heating as well?

Good — the halogen spot is the right approach and 33–34°C is close, nudge it to 35°C if you can by raising the bulb slightly or going to a 75W. The UV side is where the real damage has been done and that's what we need to fix properly. I'd recommend the Arcadia T5 HO 12% UV tube kit — specifically the 54W 1200mm version for a 120cm table. The 12% output is designed exactly for Mediterranean tortoises like Hermann's, producing a strong UVI 3–4 in the basking zone which mirrors the intensity they'd get in the wild. Mount it inside the enclosure, at around 30–35cm above the tortoise, and run it for 12–13 hours a day on a timer. You'll need the Arcadia T5 controller unit to run it — it often comes as a kit. Within four to six weeks on proper UVB you should see a real improvement in activity and appetite as his D3 levels recover.

A short-term D3 supplement is a sensible bridge while his levels recover — I'd use a calcium plus D3 powder dusted lightly on his food three times a week for the first six to eight weeks. Arcadia EarthPro CalciumPro Mg is well formulated for this. After that, once the T5 12% is doing its job consistently, drop supplemental D3 back to once a week and rely on the lamp for the rest — over-supplementing D3 long term isn't good either. The lamp is the fix; the supplement just helps him catch up faster. One last thing: replace the T5 tube every 12 months even if it still looks bright — UVB output degrades well before visible light does, which is exactly what catches people out with cheaper bulbs.

That's the right call and he should respond well to it. Get the basking spot up to 35°C, run the T5 on a 12-hour timer, and dust food with calcium and D3 for the next couple of months. If he's still notably lethargic after four weeks on the correct setup it's worth a vet check to rule out any secondary issues, but in most cases like this the turnaround once proper UVB is introduced is quite clear. Good luck with him.