Sounds normal. They need a lot of water now. Don't let the coco get dry
Actually, CANNA recommends keeping the medium a bit dry. The following excerpt is taken from canna's member only section, I highly suggest signing up and reading every peice of literature they have available. It really helped me in my garden:
"Coco retains an enormous buffer of water and nutrients. It is recommended that the grower keep the medium a bit dry rather than soaking wet. Wet circumstances form an ideal basis for fungal diseases like Pythium. A drier substrate passes more air through to the roots stimulating them to absorb water and nutrients more actively. This results in a faster growth and higher yields.
Another important instrument is timing. Once the Coco has become too wet, reduce or pause watering until the Coco has dried out and then start normal watering again. Check the moisture content of the Coco by hand or by determining its weight by lifting the pot or slab. A rule of thumb for watering fully-grown plants is 4 to 6 litres per m2 a day. By decreasing the dripping frequency and by increasing the amount of nutrients per watering, the best use is made of available water and nutrients. This will also improve drainage. The frequency of watering depends on the evaporation and the water supply in the Coco. A common rule is that one daily watering is sufficient during the first few weeks under normal circumstances; then increase up to 2 times a day; 2 hours after the lamps have been turned on and 2 hours before they are switched off again.
Please keep in mind, smaller root volumes per plant (small pots or many plants per slab) will make Coco dry out quickly. Therefore it is critical to water these plants more often."