[dantra]

Actually if you use Duplarit G (I think its G) the laterite is in a glandular form not power so it won't turn your water red at all. You can use Duplarit K which are balls of laterite (smaller than a golf ball size) and shove that under the plants. The cheaper laterite is in powder form, (you get what you pay for).

Obviously you would use the Duplarit G under your substrate.

Whatever you decide to do I hope it works out for you

Dan