Make SIS BETA fuel yourself just a few pence per bottle

I use a ready-made drink with carbohydrates and electrolytes. One scoop of this drink has 370mg of sodium + I also consume a gel that has 200mg of sodium…
So in total about 550mg of sodium…

I lose about 1000ml of water per hour of hard training, so I think 500mg of sodium is not enough…

Can I simply add 1000mg of table salt to this drink (400mg of sodium)??

Should I pay special attention to anything?