HFT is only one type of algo trading. You can make money with simple trend following algos that execute perhaps only a few times a week. To the OP, if you are

HFT is only one type of algo trading. You can make money with simple trend following algos that execute perhaps only a few times a week. To the OP, if you aren't sure about market execution, it makes me think you haven't modeled for slippage. Make sure you do, as that nudges many profitable algos into the red.