A description of the problem and any of these following questions they can answer.
1. Soil or Hydro?
2. If hydro what type bubble, ebb and flo, etc.?
3. ferts/nutes used? Soil mix?
4. Lighting: Florous, HPS, MH, or mix? wattages?
5. PH if known?
6. What stage of growth?
7. Relative humidity and temp of area if known?
8. Grow area size and ventilation?
9. Any other measurements that may be useful like PPm, EC, CF, etc.?
10. lighting schedule?