Woah - Wait there len, let me see if i can sort you out with some good advice on canna coco.
I'll grab you some links, but first of all
.. don't rinse the coco!! ^_^ (this feedback is from the people who make it! ^_^ )
Back in a couple of mins
edit 1:
https://www.autoflower.org/f126/[canna]-coco-growing-tips-29173.html MUST READ! Never plain water and some watering tips.
Good all round general info taken from the Canna Members area how to's and coco advice.
edit 2: As for watering, less is more at the seedling stage, so a very rough guideline is about half a glass (a normal, not pint glass) of water should last about 4-5 days in normal growing conditions (75-80f 40-50%RH)
I presume you will be dropping the seed into it's final pot.
When the plats are established with decent roots, you'll be able to water by the weight of the pot. Just pick it up when fully watered and it'll be super heavy. Wait until it is light. (Canna recommend watering at 50% weight...although personally i wait longer)
Do you have an EC meter?
Watering at less than 0.8ec will ruin the buffers in canna coco.
The buffers in Canna coco are pretty awesome. your pretty much fine watering between 5.5ph and 6.2
although i'd work it so your more acidic for veg and creeping up to the 6.0 -6.2 for flowering.
If you don't have an EC meter. You'll have to take a guess.
My water has a background of about 0.5ec so if i add 1ml of coco A&B to about 2 litres of feed, i'd expect it to be in the range of 0.8-1.0 (which will be fine for your seedlings)
If you have some Rhizotonic, it's awesome too, the roots will love it. If you make a PH mistake and go too acidic, you can use a few drops to bring the PH back up without effecting the EC

(sweet!)
Hope this helps
All the best
Blue ^_^