i just use the gravel. they have weights and they are lead. there a lot of gravel type food stuff. some better then others. any one you were looking at?
If you do not have enough substrate to hold the plants down, you may not have enough substrate. That is not a tautology. Substrate has many benefits and it's good to have a few inches. Someone gave me my tank and there is about two inches in there. If I set it up I would have done three.
from what i understand (we had a thread about this a few months back) they are made of zinc. they stopped using lead in anything decades ago. I use them in my tank, no problems at all. The only concern is that they tend to make stems rot, due to bunching, and lack of light.
It discusses how things that say "lead" don't actually contain the element Pb.
I don't know what to think. But none of my fish have reacted adversely and I've been using them for a couple years. I am trying to get more professional about my plants, tho, by switching to a plant substrate so hopefully I won't need to use weights anymore.