Crushed Coral

[Built2Prfctn]

My water is pretty soft in my area and wanted to prepare the tank for Rainbow Fish. To harden my water I was going to add crushed coral substrate in my filter. Has anyone had success doing this?

 

[Byron]

I have done this but it is not effective, for two reasons. The pH will rise, and significantly, but the GH is not affected. You need to increase the GH in order to effectively increase pH, and for fish that require a basic pH they also usually need moderately hard (or harder) water, so the two go together. The GH is the more important of the two because the mineral in the water is essential for the internal physiology of the species.

Second problem is that crushed coral is calcium, but to increase GH and pH effectively for fish you need calcium and magnesium, and dolomite or aragonite provide both. I have used these as a substrate for hard water species. However, you have to be careful because you can raise the parameters too much. There is a lot to sort out when fiddling with water chemistry.

First you need to know the actual GH, KH and pH of your source water. Once you/we have those numbers, you can work out how best to raise the GH/KH/pH.

 

[Built2Prfctn]

I have done this but it is not effective, for two reasons. The pH will rise, and significantly, but the GH is not affected. You need to increase the GH in order to effectively increase pH, and for fish that require a basic pH they also usually need moderately hard (or harder) water, so the two go together. The GH is the more important of the two because the mineral in the water is essential for the internal physiology of the species.

Second problem is that crushed coral is calcium, but to increase GH and pH effectively for fish you need calcium and magnesium, and dolomite or aragonite provide both. I have used these as a substrate for hard water species. However, you have to be careful because you can raise the parameters too much. There is a lot to sort out when fiddling with water chemistry.

First you need to know the actual GH, KH and pH of your source water. Once you/we have those numbers, you can work out how best to raise the GH/KH/pH.

PH 7.2
GH 85
KH 40

How can I add dolomite or aragonite?

 

[Byron]

PH 7.2
GH 85
KH 40

How can I add dolomite or aragonite?

Presumably those numbers are in ppm (or mg/l which is the same), so GH at 85 ppm equates to 4.7 dGH (call it 5 dGH). And KH of 40 ppm equates to 2.2 dKH (call it 2 dKH). The pH of 7.2 is thus likely over time to lower as the water becomes more acidic in an aquarium. The KH is what "buffers" pH, but here its capacity is small so I would expect the pH to lower in time.

Doing nothing, you have ideal conditions for soft water species. That does make life very much simpler for water changes, both the regular 50-60% and any emergency ones. Having to prepare water in advance may sound easy but it is involved.

Which is why I preferred the substrate method when I needed a tank of hardish water. A substrate composed of aragonite is the easiest. You can buy aragonite based sands for an aquarium. The only problem here is that it will raise it quite a bit. This is straightforward for rift lake cichlids and livebearers. Before using it for rainbowfish I would want to test it out.

I did add some to the filter once, but it raised the pH astronomically but did nothing for the GH as it was too small an amount. This works to buffer pH, but not for providing suitable harder water for fish requiring this. My GH is zero, the pH used to be below 5 in the source (tap) water and the small amount of dolomite or aragonite in the filter kept the pH around 6.5 but did nothing to the GH, which solved my problem because I wanted the soft water but with a slightly higher pH. This would not work for harder water fish.

There are also the mineral salts intended for rift lake tanks. "Salt" does not mean common table salt, sodium chloride, but the salts of minerals like calcium and magnesium. [Just to be clear, sodium chloride (common salt) does not raise GH and it is harmful to all freshwater fish long-term.]