Controlling Mold on Your Tipi
Mould will grow on canvas even with a mould resistance and waterproofing agent if the Tipi canvas is not aired and dried regularly.
Roll the sides of your Tipi up regularly especially if you are going through a winter. Don’t let water pool or dew touch your canvas. If mould has been allowed to grow this seems to be a way of getting rid of it. The mould must be treated at first sight and not allowed to grow further.
Chlorine bleach, mixed 1:8 with water and applied with a scrub brush: The winner, although it did require some elbow grease. The scrubbing helped work the solution into the weave, which helped it make contact with the deeper parts of the stain.
The trick here is patience. It sometimes takes ten or fifteen minutes for the bleach to work. The worst areas had to be done two or three times. There was a little residual discoloration, and significant fading where the painted areas were treated. I recommend soaking all the fabric, not just the parts that got mildewed, because otherwise it's very easy to see the parts that got spot-treated because they're much whiter than the adjacent sections (except for the specific areas that were worst affected by the mildew stain).
I also recommend using rubber gloves on your hands to avoid skin irritation. I didn't, and wished I had later when the chlorine left reddened areas on my fingers that looked a little like first-degree burns.