Acid Washing Key Largo Rocks

[sahin]

OK, so I bleached and then acid washed my Key Largo rocks from Marcorocks.com.

After I washed the rocks in muriatic acid (hydrochloric acid) I noticed that some of the smaller pieces which stayed in the acid water longer have turned bone white. There was lots of bubbling etc during the process.

I have a few questions:

1. Are the whiter looking rocks cleaner in terms of phosphate and organics?

2. The acid water turned very much pee colour-is this a sign of organics/phophates etc taken off the rock surface by the acid and into solution?

If the answer to the above questions = yes, then I am minded to acid wash the larger and darker looking pieces again.

It is an easy process for me, but I am only wanting to go through the process if there is real cleaning taking place or that the rocks will clean up even more if I do another acid bath.

The reason for posting in this forum is because I want to know what is chemically happening and would prefer to have an answer from a chemist, rather than a hobbyist who may be just guessing - I dont mean any offence by this; I simply want to know the accurate scientific reason and what the acid is exactly doing.

Many thanks in advance.

[bertoni]

1. They likely are more pure calcium carbonate, but the coloration of the other rocks might not be organic in nature. I don't think phosphate contamination would be visible at all.

2. No, the coloration might be due to soluble mineral content.

[sean04]

sahin,

the following thread may be useful:

http://www.reefcentral.com/forums/sh...ighlight=lowes

On p.3 the following is stated:

Originally Posted by tmz

The rock neutralizes the acid as it dissolves. Calcium carbonate( which is about 96% of your rock substance) dissolves to carbonate and calcium at lower ph say around ,7.7. The dissolved carbonate (CO3 )is basic and adsorbs H+ as a large portion of it becomes bicarbonate HCO3 thus neutralizng the acid. As the rock dissolves it fizzes .So the instructions start with fresh water add and wait untill the fizzing stops which is when the water should have reached a ph high enough to stop the rock from dissolving further.

Adding extra acid to the tank will lower ph as it is acidic( high in H+). So testing the ph of the water holding the rock should give an indication of the presence of acid. A good rinse to remove dissolved rock is necessary.

[sahin]

Originally Posted by sean04

sahin,

the following thread may be useful:

http://www.reefcentral.com/forums/sh...ighlight=lowes

On p.3 the following is stated:

Thanks for that.