Iron on Slate Tiles

Hoagii · Jan 4, 2016

Hello all. I recently purchased some slate tiles from a hardware store in the hopes of adding them to a new tank I'm setting up. I've caught some snippets here and there about iron in slate tiles and how "red slate" or "red veins" in slate should be avoided.

The tiles I got were packaged together so I wasn't able to see them all before buying them. When I opened the package, I noticed that several tiles are black on one side and red on the other. The red sides had a lot of reddish dust that came off when I scrubbed them.

So my question is how I can tell if it's truly iron and I shouldn't use them? I've attached some pictures if it helps. Is this a normal look for slate? Or is it dangerous iron?

AxolotlChris · Jan 5, 2016

Each type of slate from around the world has a different mineral makeup, those slate tiles in the images have the reddish rusting vein covering the underside so are not safe for your aquarium as they will leach contaminants.

You need inert slate, you can test whether the slate is chemically inactive by pouring vinegar onto the slate to see if it fizzes/bubbles.

Its also always best to scrub and clean using boiling water on any new rocks that you are placing in your aquarium to sterilize them.

Look for slate which is a solid deep grey color without and odd coloration.

Read this article on 'Safe Slate' Safe Slate for Aquariums

Mark · Jan 5, 2016

I believe the iron found in slate is iron oxide (Fe2O3). People add iron oxide to fish aquariums as a plant fertiliser so I don't know how dangerous it is to aquatic life. I've used red coloured slate in newt tanks for many years with no apparent problems. The composition of slate varies but the iron oxide content is typically 4-8% - irrelevant of the colour.

AxolotlChris · Jan 5, 2016

This article contains further information on rocks and sanitizing them: Axolotl Sanctuary
It also mentions that iron oxide can damage filters, im not sure if this is the same as what is within the slate though.

There does seem to be lots of information on how iron oxide is not harmful to fish is small quantities, but I'm not sure how it would affect an Axolotl which absorbs through its skin.

AxolotlChris · Jan 5, 2016

This appears to be a good article also: Suitability of Rocks in the Aquarium - A Practical Guide

Hoagii · Jan 5, 2016

I guess I'd rather be safe than sorry. Bummed that I'll be pitching half of the tiles :/

I will say that I sprayed vinegar on all of the tiles and did not get a single reaction. I dunno if that changes anything.

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