Watering

Depends on your pot size, you could always find some good soil the very good absorvent kind and make a mud mixture, not too much muddy, just enough to cover the sandy soil as the muddy water goes thru the soil. It will improve the water retaining but as you water after that it will start washing away slowly. You can just pick up regular soil and give it a hard mix with water and the muddy water will form along with some sandy residue on the bottom. For your current soil you don't want to wash away all the nutrients with too much water, giving 1.5l in a 0.45l pot its basically flushing everytime you water. Have you thought of using a big water bottle and poking a needle sized hole on the top and another on the bottom and leaving it dripping automatically over the course of the day into the soil? Drip method seems like could do wonders there. Best of luck growmie.