I'm trying to lower the KH in my aquariums by adding RO water, but it seems stuck at 6-8. I'm thinking the problem might be the gravel/rocks. Are there any types of aquarium gravel that can raise KH? Also, can filter carbon raise KH?
crypticmonk
Hi crypticmonk,
The short answer is definitely "Yes". A lot of gravel is epoxy coated or 'painted' and the underlying stone may be the issue. If it were me I would remove any 'rocks' that are part of your decorations and then see if you can lower your dKH. If so then you found your culprits(s).
The short answer is definitely "Yes". A lot of gravel is epoxy coated or 'painted' and the underlying stone may be the issue. If it were me I would remove any 'rocks' that are part of your decorations and then see if you can lower your dKH. If so then you found your culprits(s).
Mineral rocks are definitely known to raise kH and gH. I suppose some types of gravel can as well. A good way to test is place some of the gravel in a container with just RO water. See if the kH rises.
Carbon shouldn't raise or lower kH as far as I know.
Carbon shouldn't raise or lower kH as far as I know.
There are several groups of substrate.
Clay based products such as Oil Dri, Turface, Safe-T-Sorb and kitty litter. The details of each may vary (some fall apart faster than others, some have other issues). In general they can remove the KH from the water, and this allows the pH to drop. Most have high cationic capacity which is good. Means they hold the fertilizers in a way that plants can use them.
Specific plant substrates like Eco Complete and several of the Flourish product line, and others. These may have high CEC, and usually do not raise the GH or KH. Eco Complete made a product several years ago that did increase the water hardness.
Aquarium substrates intended for Rift Lack Cichlids or Marine tanks will almost always raise the GH, KH and pH. Coral sand, Aragonite and others, often limestone based.
ADA products usually remove the KH.
Neutral products not specifically for aquariums: Sands such as pool filter sand and blasting sand. These are graded so all the particles are the same size, and work well in an aquarium. Black Diamond is one brand of blasting sand.
Landscape gravels vary. Often they are shipped all over the USA, but called different things in different areas. The best way to find out about these is to go to your local brick, stone, soils, masonry or similar yards where they sell these materials by the truckload. They will often sell it in bags, too. Take some zip lock bags and a sharpie. Get a handful of whatever gravel or sand you like and label the baggie. Then take those samples home and test them in a glass or jar of water. Whichever do not affect the parameters (GH, KH, pH, TDS) after several days to a week are generally aquarium safe.
Clay based products such as Oil Dri, Turface, Safe-T-Sorb and kitty litter. The details of each may vary (some fall apart faster than others, some have other issues). In general they can remove the KH from the water, and this allows the pH to drop. Most have high cationic capacity which is good. Means they hold the fertilizers in a way that plants can use them.
Specific plant substrates like Eco Complete and several of the Flourish product line, and others. These may have high CEC, and usually do not raise the GH or KH. Eco Complete made a product several years ago that did increase the water hardness.
Aquarium substrates intended for Rift Lack Cichlids or Marine tanks will almost always raise the GH, KH and pH. Coral sand, Aragonite and others, often limestone based.
ADA products usually remove the KH.
Neutral products not specifically for aquariums: Sands such as pool filter sand and blasting sand. These are graded so all the particles are the same size, and work well in an aquarium. Black Diamond is one brand of blasting sand.
Landscape gravels vary. Often they are shipped all over the USA, but called different things in different areas. The best way to find out about these is to go to your local brick, stone, soils, masonry or similar yards where they sell these materials by the truckload. They will often sell it in bags, too. Take some zip lock bags and a sharpie. Get a handful of whatever gravel or sand you like and label the baggie. Then take those samples home and test them in a glass or jar of water. Whichever do not affect the parameters (GH, KH, pH, TDS) after several days to a week are generally aquarium safe.
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