substrates and hard water ( reactivity??? )

[Magnum Man68 182]

so I’ve noticed something in a few of my well water tanks… with normal river rock substrates ( brown hues ) things look normal, but I have several tanks with both hard and soft water, that use a polished black river rock… I’m unsure the rock material, but it seems to be attracting the calcium and iron from my rock hard well water… in several years the black rocks have remained as polished black rocks, in my soft water tanks, but the hard water tank, that has the same substrate, it appears as if the calcium and iron are attaching to the rocks, as it doesn’t gravel vacuum off, and they are looking more grey / brown, in half the time that that rock has been in my soft water tanks… it makes me wonder if it’s an ion thing, and the rocks are attracted to the calcium and iron in my hard water??? thoughts…

 

[Magnum Man68 182]

this is the type rock, of course they don’t list the type of rock it is, but, it doesn’t appear to be a slate based rock.. and I always wash it before adding it to tanks, just in case there is any polishing residue…

https://www.amazon.com/dp/B0BV38CGVS?tag=fishforums-20

 

[Jennet47 105]

Have you tried looking at this??

https://iere.org/animals/what-are-the-black-rocks-in-my-fish-tank/

Best Black Rocks for Fish Tank Accessories That Brighten Every Aquarium – Pawbamacare — Pet Wellness & Insurance Guide

7 Best Aquarium Black Rocks for [YEAR] - Aqua Revolt

A guide to the 7 best aquarium black rocks for [YEAR] reveals hidden benefits and stunning designs that will transform your tank—discover why they’re essential.

www.aquarevolt.com

Nothing I have been able to find previously when looking for black rocks gave me anything that was smooth and fairly large, I'm afraid. At least not at a price I was willing to pay for. And as for Amazon, well, we can only go by other peoples reviews, and they are often only from people who have not posted long after they first had them.

Is that why you are asking in here? I would certainly like the question answered also, as I like black rocks, but have been wary about buying anything that may affect the water, although my water appears not to be quite as hard as I first thought.

 

[Magnum Man68 182]

these pictures are the same rock…

1.5 years in hard water…

3 years in soft water… ( sorry, both are in need of a vacuum )

 

[Jennet47 105]

Hmmm.... can clearly see what you were asking from the pictures. It does not look anywhere as black as the stones in the amazon links, and they look like bigger stones in your tank.

I used more of a mixture of rocks in the very distant past when I had aquariums. although many of them looked like the dark grey type you appear to have in your aquariums. And I used gravel based substrate and only used beach cobbles for bigger stones. Also, water testing was not that big over here in the 70's, so unless fish had problems, we did not tend to do it.

However the rocks in the hard water tank do seem to have some scale attached to them unless they are different types/colours of rocks I am seeing.

Do the waters test differently chemically in any way?

 

[Magnum Man68 182]

waters are quite different now, as the soft water tanks incorporate RO water, and the hard water tanks are rock hard alkaline well water…

 

[Uberhoust13 3]

If I remember correctly you are using well water. It is quite possible for the temperature and pressure your well water is saturated, but as it warms and the CO2 degasses into the atmosphere you end up with a supersaturated solution of carbonates (oversaturated). With the KH minerals the solubility is controlled by the CO2 concentration as well as temperature (well water can initially be high with CO2). The carbonates leave solution because the CO2 concentration drops too low, resulting in the carbonates leaving solution and depositing on the rocks. In the softwater tanks the concentration of carbonates is already well below the saturation point so this would normally not occur.