Tips On This Rock?

[hudsona85]

I apologize in advance for the somewhat long post. I went to one of my favorite LFS and as usual oohing, ahhing, and drooling over the fish. I proceeded to ask one of the guys there I've known for a good while about the slate rocks they carry. I wanted to put some in my 75gal to help create the look I want to go for. At $1.99 per pound it could add up pretty quickly! So he told me of a landscaping place that usually charges for .50 per pound and that is where they get theirs from (of course he told me not to tell anyone about this). At any rate, I went to said place and asked the lady about slate rock and told her the reason why. They sold them by the pallet but she said there would be a broken pallet out here and just take what I needed. Even better, she gave them to me for free!
 
Now, here is the part where I would like some take on ideas. I split up the rocks into 2 5 gallon buckets and filled up with hot water (not boiling) and API tap water conditioner. I dump the water out every 2 days and refill it with hot water and the conditioner. Today I took whatever brush I could find to see if I could scrub it down. Of course with it being outside at a landscaping business, there was a bunch of debris on it. I know I need to get a stiffer brush to get stuff off it but there was at least 1 rock I noticed some orange specs. My first thought is rust? IF that is the case, does that mean that there would be some kind of metal in there? I took a picture of it to explain what I am describing. Does not seem to be much of it and it could be just part of the rock. I rather ask than make sure.
 
Also, is there anything else I could do to make sure this is safe for the aquarium? I think I read somewhere in another forum to test out the rock with the API Nitrate #2 and see if there is any kind of reaction and didn't notice anything on there. I plan to have SA Cichlids and other soft water fish in there.

 

[eaglesaquarium]

Pour some white distilled vinegar over it.  If it fizzes, it will change the water chemistry and be a problem... if not, it is likely fine.  
 
 
Another option is not to test the nitrates but to put the rock into a bucket of water and test the TDS before and after a week.  If there is a sharp increase, that's a problem... if the TDS are pretty much the same after a week, its safe.  

 

[Akasha72]

I have lots of slate rocks in my tank that my Dad gave me. They've been absolutely fine but I agree with Eagles, just check them first

 

[eaglesaquarium]

Are they slate?  Couldn't tell by the pictures.  I use slate all the time.  Perfectly safe (depending on what they have been exposed to in the past). 
 
 
EDIT:    it said slate a bunch of times in the OP...  silly me.  That's what I get for multitasking.

 

[hudsona85]

Pour some white distilled vinegar over it.  If it fizzes, it will change the water chemistry and be a problem... if not, it is likely fine.  
 
 
Another option is not to test the nitrates but to put the rock into a bucket of water and test the TDS before and after a week.  If there is a sharp increase, that's a problem... if the TDS are pretty much the same after a week, its safe.  

 

I have lots of slate rocks in my tank that my Dad gave me. They've been absolutely fine but I agree with Eagles, just check them first

 
I actually have slate in my 55gal and work just fine. This slate that I picked up was picked outside at a business. My concern was to make sure there was nothing in this kind of slate that would do any harm which was the reddish/orange color. I will test the slate with vinegar and see what happens. I don't have a TDS meter but probably should invest in one. I used the API nitrate #2 on the actual rock to see if there was any reaction to it.  (I was told this could be done, could be wrong). Appreciate the advice!