When I was setting up my siphon-aquarium I discovered that the local aquarium shops were grotesquely deficient with regard to lava rock. Personally, my favorite aquarium decorations are lava rock and driftwood (real wood, that is) as they are naturally porous and offer great residual-flow filtration in almost any kind of aquarium. I am particularly fond of residual-flow filtration since it is cheaper to maintain than many of the filtration systems out there and is naturally complementary to my other favorite filter type, the UGF (undergravel filter). Since the pet shops did not have any of my beloved lava rock, I went to places that I knew would carry something that was at least similar: garden and landscaping stores. At Lowe's, of all places, I found a 1/2-cubic-foot bag of red lava for about four dollars ($4). Red lava is normally used as a decorative substrate around gardens, ponds, pathways, etc, but is also aquarium-safe (provided you rinse it thoroughly in hot water and allow it to sit overnight). I wound up putting about 1/6 of a cubic foot of the red lava into my siphon-aquarium and thought that would be the end of my little decoration-finding adventure.
A few days ago, however, I did a google image search for "aquarium lava rocks" and discovered that AquariumFish.net was selling little bags of 7-10 individual red lava stones for about four dollars apiece ($4 per little bag), calling them "denitrifying lava rocks." Furthermore, AquariumFish.net claimed, "Every freshwater aquarium and fish bowl should contain the appropriate amount of Lava Rock," (para. #1) and went on to discuss how beneficial the rocks were and that careful testing of the water was necessary to produce the correct levels of nitrate in the water (AquariumFish.net suggested a range of 20-40ppm nitrate). Much of this information, in and of itself, was not bad, but I could not help but feel that it was extremely misleading, particularly for new aquarists.
What's the Problem?
Before I proceed in lambasting a well-known internet pet shop I should note exactly why I find AquariumFish.net to be so misleading. First, AquariumFish.net claimed that low levels of nitrate (below 20 ppm) could lead to the production of hydrogen-sulfide (para. #10). However, I know of many freshwater aquarists who have less than 10ppm nitrate yet do not report any problems with hydrogen-sulfide production. A while back I did a survey of over 100 freshwater aquarists and found that all of them agreed that low levels of any nitrogen compound was better than a higher level of that compound (Efficiency and Lethality: Survey Data Trends). Further, many of those aquarists had aquarium systems with negative production rates of various nitrogen compounds but the aquariums did not suffer any ill effects the aquarists felt were worth reporting. What is more, most of my own aquarium systems have operated at less than 10ppm nitrate (several below 5ppm) with no ill effects. AquariumFish.net is overgeneralizing their claims--claims that most well-established aquarists would reject. That is, if 0ppm nitrate can be achieved and it is well known that all the common nitrogenous compounds (ammonia, nitrite, and nitrate) are harmful, then the logical thing that most aquarists should strive for is 0ppm of all basic nitrogen compounds.
Secondly, AquariumFish.net has paired their "denitrifying lava rocks" with water testing in such a way as to result in greater sales of both products. Personally, I do not put a ton of stock in water testing as my experience working at the College of Southern Idaho Laboratory showed that most commercial aquarium test kits were horribly inaccurate, but I would never tell a new aquarist to omit them altogether. Test kits do have their place, but they do not have to be used very often (namely during the cycling process and about once every two weeks). AquariumFish.net, in asking aquarists to submit to the idea of a special balance of nitrate levels (20-40ppm), is effectively asking aquarists to test their water more often than would be needed otherwise (i.e., the case that the aquarist knew all the nitrogen levels were near 0ppm because of how the system was maintained).
Lastly, AquariumFish.net is severely overcharging for their product. If I were to take my red lava bag from Lowe's and distribute it in the portions AquariumFish.net uses, I could easily make a 30-dollar profit per bag ($30/bag), which is about a 750% profit margin with regard to the cost of the materials. This ridiculous price hike is made worse by AquariumFish.net's implication that their lava rocks are the only ones to buy:
While much of the information in the preceding quote is accurate in that one does have to be mindful of chemical contamination and be aware that not all rocks are suitable for aquarium use, AquariumFish.net's meaning is quite clear: Only their rocks are selected to yield the desired results. This is not true, at all, in that I have gathered my own rocks on several occasions and have never had any problems (granted, I am probably better at picking out safe stones than the ordinary layman). Moreover, I have had nitrate-reducing results from many types of lava rock, not just red lava and certainly not AquariumFish.net's lava rocks.
In short, this is an instance in which the aquarist should be wary. Generally speaking, if you can find it in a pet shop, you can find it for at least half the price somewhere else. In many cases it is worthwhile to pay the extra money a pet shop (or internet pet shop) may charge in exchange for the security of knowing that the product is fish-safe and guaranteed to work, but "denitrifying lava rocks" are not on the list of such cases, especially given that regular red lava is so much cheaper. Additionally, lava rock is by no means a necessity, as AquariumFish.net implies, for removing/reducing nitrate--aquarists with planted tanks have been doing such for years (like nearly a century) without the aid of lava rock.