I've heard before that fish in the wild will often not have food during certain times of the year due to a low supply. But it seems that the lake situation might be different. My understanding of lake Malawi is that it is "fairly" stable all year round. There are some minor fluctuations in temperatures and day length but nothing drastic. It seems to me, therefore, that the food supply would be fairly stable.
I have used Aquatrol Spirulina 20 for the last seven years or so. It's all I use and I usually feed them a little twice a day ... morning and evening. I don't think I've had any problems related to diet thus far.