Can you use lime mortar as cement (with sand/crushed shell/coral aggregate) as a mortar for diy rocks? Portland cement seems to have so many unknown additives ?
Yes you can use Portland cement to make diy rocks. But it must soak in a river or for a few months. Or change the water every day in a bucket for 2-5 months. The purpose is to reduce the high ph that the cement will leak into you tank and kill everything. Lots of diy threads about this. Not worth the time or risk imo.
Yea you can use the cement from marko rocks. Also GARF has all the info on how to do it. They've been doing it for years.
Of the top of my head I don't remember the Portland cement you want. I belive it's a plasticizer in one blend. It's not an unknown at at.all. Just a lot of myths.
The marko is a Portland and we use it in tanks all the time. Visit the website.