Black water habitats are slow moving waters located in rainforest areas. Over time decaying vegetation releases tannins that stain the water brown and make it soft and acidic. Fish keepers who wish to recreate a Blackwater habitat in their aquarium may use black water extract to help adjust the water to the appropriate conditions. When using additives, keep in mind that you will have to treat the water regularly to maintain the desired water parameters. The cost of regularly using such additives can be significant. However, your fish will benefit regardless of the method used.
Tetra Blackwater Extract contains trace elements, vitamins and most importantly, peat extract. The effect is not as dramatic in terms of tinting the water, but it will assist in lowering pH and reduce hardness. It is particulaly useful when attempting to breed fish that prefer soft acidic water. As the best known name in Blackwater products, Tetra Blackwater Extract often gets blasted by those who believe using extracts is not the preferred method to achieve Blackwater conditions. However, I've found that it performs well and is as reasonably priced as any additive on the market. An 8.3 ounce bottle will treat 250 gallons. Be sure to comparison shop as prices vary.
Amazon Extract Cichlid is composed of humic acids, tannins and other organics. Notably absent is peat, and the product states that it "does not alter pH". That is not a show stopper if you already have stable acidic water, but it is an important factor to consider when choosing a Blackwater product. The organics will help soften the water and promote coloration in the fish, as well as facilitate breeding. An 8 ounce bottle that will treat 475 gallons. Cost is reasonable, but can vary, so do your homework before making a purchase.
Marc Weiss touts his product as encouraging fish fertility and lush plant growth, while at the same time discouraging parasites and the growth of algae. To date, I have not seen actual data that supports these claims, but many fish owners swear by it. The product does contain Ketapang leaf, which has a long track record of lowering pH and removing heavy metals from the water, as well as stimulating spawning in rainforest fish.
Peat is my personal favorite for softening water and maintaining a stable pH. Sea Super Peat is an easy to use peat product. It can be added to virtually any filtration system, and will lower both the carbonate hardness and pH of the water. Sea Super Peat will tint the water and gradually release trace elements that promote fish health. Often used in conjunction with other products to achieve a stable pH.
Seachem Discus Buffer is a good product for lowering pH, as well as softening the water. When using a product such as this one, keep in mind it will have to be used for every water change, and when topping off water. It will also be necessary to use another product to add trace minerals to achieve the desired water conditions. Also important to consider is he fact that it is not recommended for tanks with live plants.