So after getting my hardness test kit (previously I'd been relying on city water tests) I found out I have much softer water than I originally thought. Tap is 3 GH and 2 KH. Great for my future cardinal tetra, not too great for my goldfish. One of them has had chronic health problems, and I'm thinking it may be a result of the stress from my very soft water. I've been looking at methods to raise my GH and KH (I know my pH will rise, too). Right now I'm trying to decide between dolomite in the filter or Seachem Replenish. One comes with dosing instructions; one doesn't. I'm very interested in finding out how much dolomite to use. This is brand new territory for me, so I'm open to all opinions and experiences. I'm also curious where one can buy aquarium-safe dolomite.
I've also been given the suggestion of raising KH and GH by adding calcium chloride, Epsom salt, and baking soda. I've been trying to do some reading on this, but my head is just spinning. Softening water now seems so much easier. :?
The Seachem product will only raise GH as the ingredients are chlorides rather than carbonates. I wouldn't go the epsom salt/baking soda route either. Byron has mentioned a study or article about baking soda being problematic. This way is also just more complicated, having to figure out dosage for two substances.
If you want raise both GH and KH, you can do both with CaCO3, it will contribute Ca cations for GH and CO3 anions for KH. Calcite or aragonite are both mineral forms of CaCO3 (same chemically, but with different crystalline structure). Mineral dolomite – CaMg(CO3)2 – will add Mg along with the Ca and CO3. Not sure of the availability of these. Crushed coral is an option, it is just CaCO3 of organic origin.
Some use limestone, which is a sedimentary rock composed mostly of CaCO3, but can also contain extraneous substances, some that can be harmful, similarly, 'dolomite' is also used to describe dolostone, a sedimentary rock (one composed mostly of the mineral dolomite), but shouldn't be confused with the mineral as it is not just CaMg(CO3)2.
I would look and see what is available for marine or rift lake cichlid tank substrates, as its purpose is for use in aquariums. Dosage will just require experimentation, put a little in a mesh bag and put it in your filter or somewhere where the current pass over it and check the numbers, just do it incrementally with small amounts so that any change will be gradual.
I agree with what Quantum has posted. I have very soft water and have now had to raise the GH in most of my tanks (for the plants, ironically, not the fish) and I've experimented with various substances over the years.
The best and cheapest was dolomite. Years ago it was available in a gravel intended for substrates in marine tanks and rift lake cichlids, but I haven't found any locally. I tried CarribSea's crushed coral/aragonite mix, having read that aragonite is similar to dolomite. This works, but it drives the pH very high, which for me is not an option. For your goldfish it would be fine. Just a bit in the canister filter (in a mesh bag) does it. Add maybe half a cup, and keep adding a bit every few days, testing GH and pH, until you have it where you want it. And I agree, goldfish need medium hard water.
I have not used Replenish. I do use Equilibrium to raise only the GH, it has no effect on pH or KH, which is ideal for me with my acidic water fish. The magnesium sulfate will partially work, it adds magnesium and sulfur but no calcium, and a little goes a long way. This goes directly in the water, but as I say the calcium still needs to be added, via crushed coral in this situation. Baking soda is not recommended, as Quantum mentioned, Stanley Weitzman wrote that this is not a long-term solution because it offers no buffering and it increases the sodium. The latter may not be so relevant with goldfish, but the earlier methods are more reliable.
Thank you both for your in-depth responses. I, too, was a little worried about the baking soda as I'd heard it wasn't the best for raising KH. I would love to read that article if you can link it, Byron.
I'm leaning towards crushed coral in the filter now. My one concern is weekly water changes. Won't the influx of soft water lower the hardness on a weekly basis? I do 50% WC weekly and it's a 50 gal tank. I'm concerned that the fluctuation may be a bit much on the fish. Should I age the water overnight with some crushed coral in it?
I missed the calcium chloride mention before, so I guess I should have said dosing three substances, which is worse relative to the conversation. I too, think the CaCO3 method is best, at least try it first and then go to something more involved later if needed.
With that said, looking into this more reveals that even this seemingly simple process is really very complicated. One thing I've come across that may be relevant to your question is that aragonite is more soluble than calcite (the solubility of dolomite is apparently less well know) due to their different crystalline structures. My thinking is that having some aragonite in with the calcite (I believe coral is calcite) will allow the added water to harden more quickly, I'm not sure exactly how much difference this would make, but since this combination is available on the market I think it would be a good choice (paying attention to the pH per Byron's experience).
The swing in GH caused by water changes I think will just require experimentation. I would start out with a very small amount of CaCO3, checking the GH, KH, pH until they stabilize at a slightly higher level. Then do a water change and check the numbers again shortly after and compare the numbers from before and after - continue to test until the numbers stabilize again. If the initial increase was small, any decrease due to the water change will be small. This will give an idea of how quickly the numbers rebound. Removing Ca+ from the water during a water change should increase the rate of dissolution of the CaCO3. By how much I'm not sure, but it may occur quickly enough that the swing is not very drastic. Pouring the new water directly over the CaCO3 may help. Once this process is better understood, the overall hardness levels can be increased incrementally, checking the numbers before and after water changes at each level as the rate may be different at the different concentrations. Doing this with the fish in the tank may not be ideal, but if the changes are done in small increments and the levels stay within the range that the fish can handle, it should be fine. All of this may not be necessary (I also use Equilibrium, so no direct experience with this method), but it is kind of how I would approach it. We'll see what Byron's take is since he has more experience with it than I do. I know he does large water changes with very soft water.
Regarding the chemical compositions, the formulas given are what the minerals would be if pure, which is not necessarily the case in nature. In calcite (and presumably aragonite), some of the cations (Ca+) can be replaced by others, including magnesium, iron, manganese, zinc and others. So if the CaCO3 is obtained from natural sources, it will likely contain some of each of these to some extent. Apparently, calcite can occur in a high magnesium form, with the amount of magnesium equal to what is in dolomite, but since the crystalline structure is unaltered, it is still technically calcite and not dolomite.
In more than 15 years of doing 50% water changes with very soft (near-zero) tap water, and with dolomite in the filters or now using Equilibrium, I have not had any issues that I am aware of. There is also a pH shift of about .4 with each water change of course, and I just ignore all this as the fish respond so positively to the influx of new water. Quantum has the technical side of these substances grasped much better than I do.
On that article, it was a series on maintaining forest fish that appeared in TFH in the 1990's authored by Stanley Weitzman, Lisa Palmer, Naercio Menezes and John Burns. Dr. Weitzman was senior author, and his remarks on the baking soda were:
Sodium bicarbonate [baking soda] has no effective buffer action and cannot stabilize pH in the face of additional acidic waste products. Also, one must not continually add sodium bicarbonate to adjust the pH because eventually the sodium ions present will reach intolerable levels.
just noticed my Ca+ should be Ca++ or Ca2+, as it is divalent, Mg cation is divalent as well
Thank you both very much for guiding me in my decision. I'm going to go with Caribsea's crushed coral/argonite mix in the filter and keep a close watch on how the water and fish react with water changes.
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