Hi.
Alga minimalis doesn't store any nrg into body, so to get a sustainable environment going you need to give veggies some body as well as nrg. In the options panel (under genereal I believe), there's a slider between nrg and body that lets you adjust how veggies are fed. Set it to like 90% nrg and 10% body as a good place to start, and tweak as wanted.
Veggies aren't given any disadvantage compared with regular bots, actually. There's talk of making what it means to be a veggie more complicated than just the checkbox in the options panel, but nothing concrete in code yet. Well, there are some population limits for veggies that you can set in the options, which means in a lot of sims being a veggy means you don't always get to reproduce when you want to.