Rocks, fossils and plants oh my!

On a recent vacation my husband and I picked up a huge (20lb) hematite rock and a HUGE piece of horn corral with fossils in it. I've also seen these Japanese floating moss balls and some aquatic plants that we would like to use in our two axie tanks.

Does anyone know if the the hematite and the fossil would be ok for the tanks, and also what plants are safe and what are not?

P.S Sorry this should of been in the tank set up thread..

Also another general question. Axolotl size.....

Hermese my oldest axie is about two and it probably 11"-12", and since he was moved into his 55 gal aquarium he seems to be getting a bit bigger. All the pictures of axies that I've seen, they seem like they are maybe 6"-8". Anyone know what the average size of a domestic axie is?
Cedric the newest axie I have is about 4" and seems to be growing at a much slower speed.

You can check out the Caudata Aquascaping page which has a list of 'safe' rocks for aquariums:
Axolotl Sanctuary

It lists any type of coral or fossils as unsafe so I would rule that one out immediately, as for the hematite though... a search helped me find this post which is relating to play sand but might contain relevant information:

SludgeMunkey said:

Generally speaking, play sand is usually safe. The only real issue I have with it is much of it contains quite a bit of hematite and magnetite. These forms of iron are not really a direct toxic threat, but when the water chemistry in your tank crashes as this stuff has seized up the magnetic impeller in your filtration motor it becomes a problem. Good news is you can remove it all with a fridge magnet if you need to.

Click to expand...

So while the hematite might not be a direct toxic threat it's possible if it were to wear away in your tank it might cause issues with your filter. This might be a 'when in doubt, leave it out' type of situation. Maybe someone else more knowledgable when it comes to aquarium rocks will have a more definite answer for you

As for the sizes of axolotls, I currently have a female that's about 10.5" long and I think she has grown since I've had her. I've heard of axolotls getting up to 16" while some might only grow to half of that, so I wouldn't be worrying too much about it.

Do not use any of those rocks in your tank. The coral and fossils will mess up your ph and hematite could be a problem later on. I have hematite jewelry and it doesn't look happy after it gets wet. I wouldn't trust it in a tank with living animals.

Make sure any plants you use can survive the low light and cold water axolotls need. You can easily do a search for what plants would work well.

I can say about the moss balls...usually true marimo balls don't really float. Watch out for those things labeled moss balls that really aren't marimo. They usually have a string attached. I had one in my tank and it did poorly. It was fine in the warm, well lit tank it was initially in but once I moved it, it soon died. Some people keep them well in axolotl tanks...if you want to experiment it won't harm the axies.

Officially, I advise against all of the rock mentioned.