Advice on Slate

I really want to put slate into my brand new aquarium.
I have read a lot online regarding this being potentially unsafe for my tropical fish. I have also read up on the vinegar test. Is there any advice that anyone can give to me? Do i just need to wash my slate?
(The slate has come from the floor in wales)

If you are wanting to use slate tiles, then it is important to make sure they are 100% slate and nothing else- no coatings nothing artificial at all. I use slate caves and pieces of slate all over my tanks with no ill effects. I actualli get it at a local stone and gravel yards which sells flagstones. I want the shards and small piece that break off of the flags. So with a bucked I wonder through the flagstone section grqbbing what I want off of the ground.

Slate is a a type of rock often referred to as flagstone. In reality slate is a low-grade metamorphic rock. Slate is popularly used for flagstone because it is very easily split into thin layers and is extremely common and reasonably priced.

Click to expand...

I also get river rounds fron the same place. The charge me regular price for the rpounds but minimal money for the slate shards. I use this stuff in tanks with very pricey plecos inclkuding zebras and then the more expensive ones as well. I have no issues at all. I do rinse the shards well as there are trucks and loaders puffing exhaust into the yard where they deliver stuff or send out rocks, gravel, sand etc.

Slate need not be tested to see it if leaches calcium which could change one's pH and hardness. You should be able to find pure slate tiles at places like Home Depot or tile stores. Also, never use tile grout in an aquarium- it will bring death and destruction upon your stock. Btw- I use regular tiles to make a base for driftwood to heold it in place. The tile jhas a hole I drill and then I use a stainless steel screw to attach the slate. Sometime I ill use a small nylon spacer between the tile and the wood so I can bury the tile in the substrate but leave almost 100% of the wood above the substrate.

Slate rocks are normally fine but make sure they don't have any sharp edges.

As stated just above watch for sharp edges. An emery board such as used for finger nails works well for removing sharpness.

Make sure you get slate, not shale. They are different forms of the same rock with shale being the earlier form. Shale is soft and porous which is not good.

Thank you for your reply's.
I will upload a picture of the slate I have found when i get home.
I have read a lot about how it can be dangerous, i'm currently about to start the water cycle for my tank so i'm in no rush. To my knowledge, the slate is not sharp. Im just more concerned if it is releasing something into my water that i don't want it too. Is the vinegar test something i need to do?

If the slate was previously used as flooring then there's no telling what may have been put on it over the years - cleaning products, adhesive, grout etc. It's possible that there will be traces of these left, so I'd probably steer clear.

The vinegar test is really for calcareous rocks, which slate isn't.

Mikeyboy123 said:

If the slate was previously used as flooring then there's no telling what may have been put on it over the years - cleaning products, adhesive, grout etc. It's possible that there will be traces of these left, so I'd probably steer clear.

The vinegar test is really for calcareous rocks, which slate isn't.

Click to expand...

The slate was from the floor in wales it was a huge slate path (see picture below)

Okay, well, is there are a chance that it could have come into contact with things like weed killer, fertiliser, agricutural chemicals etc? You need to make a judgement call, but be mindful of what it might have been exposed to and you won't know until you try it. Give it a good soak and scrub. Cherry shrimp are very sensitive to most nasty things, so maybe buy a few cherry shrimp or get some culls off someone you know that keeps them, and once you are cycled, put the shrimp in and see how they go.

I do use rocks found in my garden. I first put them in a plastic bucket and test if they alter the water's pH & GH significantly. If it’s OK, I leave them in a large container full of water for a month or longer and change the water several times during that time before using. I do the same thing with dead tree limbs dropped from trees, including river red gum.

So the slate itself is from a road that is virtually never used a mile or so away from a beach. My guess is that its been there for years. Infact I know it has. There are no particular sharp edges on it and if there were I could remove them. Its not slate that has ever had chemicals manually put on it, this is raw slate from the welsh outdoor floor.

Whats concerning me is that i have read it can let of gases (or somthing similar) that you cant see and could be harmful.

There are two things to look at with rocks.

First - is there any contamination? Rocks from a park could have insecticide sprayed over them. Rocks from near a road could have goodness what on them from the traffic.

Second - there could be something in the rock itself which will dissolve in the water. Rocks like limestone are made of calcium carbonate which dissolves slowly raising GH (calcium) and KH (carbonate) and pH in the tank. This is what the acid test is looking for as calcium carbonate reacts with acid to make bubbles. Coral and shells are also calcium carbonate. Other rocks might have seams of metal ore in them which could dissolve in the water and depending what the metal is it could harm the fish.


Seams of metal ore should be visible, so ignore any rocks with those. Slate is not made of calcium carbonate. That just leaves contamination as a possibility.

Essjay said:

There are two things to look at with rocks.

First - is there any contamination? Rocks from a park could have insecticide sprayed over them. Rocks from near a road could have goodness what on them from the traffic.

Second - there could be something in the rock itself which will dissolve in the water. Rocks like limestone are made of calcium carbonate which dissolves slowly raising GH (calcium) and KH (carbonate) and pH in the tank. This is what the acid test is looking for as calcium carbonate reacts with acid to make bubbles. Coral and shells are also calcium carbonate. Other rocks might have seams of metal ore in them which could dissolve in the water and depending what the metal is it could harm the fish.


Seams of metal ore should be visible, so ignore any rocks with those. Slate is not made of calcium carbonate. That just leaves contamination as a possibility.

Click to expand...

So with my slate.... (just to confirm) as long as there are no sharp edges and I have washed each piece (presumably with just water??) The only issue is possible contamination?
(Sorry if im going over what you have already said) What other steps do i need to take? Im just worried about killing my fish

Yes, blunt the edges and give it a good clean, but the only way you'll know is if you try it. I'd try it with cherry shrimp first though, as they will quickly let you know is there's anything toxic in the water.

Make sure you are fully cycled before adding any creatures.

Mikeyboy123 said:

Yes, blunt the edges and give it a good clean, but the only way you'll know is if you try it. I'd try it with cherry shrimp first though, as they will quickly let you know is there's anything toxic in the water.

Make sure you are fully cycled before adding any creatures.

Click to expand...

So in order to have slate the reality is... I have to do the full water cycle, then add only cherry shrimp, and then if theres an issue id have to remove the slate a presumably restart over again as the water would be contaminated?

You could always test the slate in a bucket of water rather than risk contaminating the whole tank. You'll need a fish-only* brand new bucket, so use that. Let the slate stand in a bucket of dechlorinated water (that is, add water conditioner to the water) for a few days for any contamination to get into the water, then try the shrimps in the bucket. Or maybe a bag of live daphnia from a fish shop.


* Don't let anyone else use the bucket for any reason whatsoever. No washing the car, mopping the floor etc.