How many psi do you put in your tube or toon

[KAZUALT]

I was just wondering how many psi is the right amount for a TU Colorado Toon. I lost my instructions years ago. I know that after a while in the sun the psi climbs abit, but what is the proper amount to start with. I usually just pump it up till it "feels full'. But is there an ideal pressure. I also realise that it depends on the boat, weather, ect.. Just looking for a ball park figure.
Also just as a laugh, has anyone ever tried helium. I know this sounds stupid, but I never claimed to be the sharpest knife in the drawer.
KAZUALT
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