What is the name of the stain you used?

Sorry to have taken so long to answer. Name of stain is CIL semi transparent cedar colour stain. Is what they call a hybrid, water and oil based if that makes any sense.

I have almost the exact same problem as you. I too stained my deck on a hot day. I did not sand it properly before hand, and I ended up with blotchy areas as well as water stains just two days later when it rained. I used a stain remover followed by a neutralizing agent. The brand I used was Benjamin Moore; it can be found at just about any hardware and paint store. You live in Canada but you don't say where. I live in southeast Alaska; lots of rain where I live. I've successfully removed all the stain along with the water stains and blotchy areas, and am now looking for a stain that will bring out the natural beauty and protect the wood. I was told to only use a latex based stain and NOT an oil based one. Maintenance was the main reason. Anyway, I would recommend the Benjamin Moore stain remover and neutralizer. It worked great for me.