I have about 15 stems of staurogyne repens and I cannot figure out a way for the plants to stay planted in my eco-complete substrate. Out of the 15, about 10 will become dislodged and float to the surface within a day or two. I've tried sticking them down with tweezers as deep into the substrate as possible but no luck so far. Is there a trick to having them stay planted? Eco-complete seems a little too coarse. Is there some sand or finer substrate I can use with eco complete?