Mix up 1L worth of your nutes, give your plants how much ever they need, throw the rest away! If 1L is WAY too much, mix up 1/2L using 1/2 the nutes you would use for 1L... and do the same. Your pot SHOULD have drainage holes - so also put a saucer underneath so that if you water it too much, it will just spill out into the saucer and you can dump it from there. Good luck with your grow!