I recommend you daytrade using Paxful.com to double up your ROI
Day trading with $200 and with paxful? It has a limited choice of coins so its not so wise to day trade on it. Adding $200 per month and using it for buying bitcoin will be the best choice of all.
I am not sure about this because I really don't know how we can double up our ROI. I think it is better to buy some of the coins and hold it for a while and sell when the price increases. at least, we have $200 per month to invest our money so we have much of coins that will bring a good profit in the future. or he can buy bitcoin only and never use it for another purpose and waiting until the price increase.