By Donna M. Recktenwalt
We’ve all heard the advice that regular partial water changes are the best way to keep our fish healthy, happy, and (hopefully) breeding. We’re encouraged by the “experts” to change tank water regularly and often.
But are there, perhaps, times when this advice is not wholly correct? when a certain amount of “benign neglect” may be beneficial?
There is at least anecdotal evidence that for some species regular water changes may not be the best of advice.
“I have [had] continued positive experience with dirty tanks and better egg recovery,” says Charles Harrison. “Water changes every five to seven days, without disturbing the tank setting or removing much of the debris or disturbing the mops, has often resulted in more eggs. My cleanest, most pristine mops and tanks don’t produce nearly the number of eggs and fry as do the more mature tanks, independent of size.”
“I have kept dwarf cichlids and know … that when the water is changed every two weeks (30% change) this triggers … the fish to spawn towards the end of this period,” comments Nancy Graham.
“I, too, have found ‘dirty’ tank conditions a boon to breeding fish and raising fry,” observes Joe Gardner, who uses exclusively sponge filters in all his tanks. “I look at good mulm in the same fashion I regard good garden compost. It takes a while to cultivate but is worth the work and wait. I have found that with various killies, livebearers, cichlids and gobies, the fry hide in the mulm and find food [there]. It is important to continue to make water changes, but not to disturb the mulm very much.”
“It seems I get more eggs (consistently) out of tanks that are in need of cleaning than those that were just cleaned,” observes Will Wasserman. “Does the polluted water cause an acceleration of egg production?”
“Bob Earls up in Creemore, Ontario, used to start out with three or four trios [of SJO] in a 15 [gallon tank] and feed heavily,” reports Richard Sexton. “The dirtier the water got, the more eggs he got.” When the fish finally got sick, he’d change the water. “The fish would be fine, but they’d never lay another fertile egg. Not just the number of eggs, but the fertility was a function of filth. The dirtier the water, the more fertile the eggs.”
Ron Harlan speculated that there might be a chemical or hormonal trigger [in dirty water] that relates to fertility and egg production. From an evolutionary standpoint, this might make sense, since fish that laid many fertile eggs in an evaporating (i.e., more polluted) pond might be evolutionarily more successful simply by producing more fry and providing a greater chance for survival of the species.
“One theory is that as the water gets dirtier, the pH drops, making it more acidic, which could also be the trigger the fish need to spawn,” says John De Luca. “I have found that about 30% of the species I keep won’t lay well until the water is dirty. I first discovered this by accident when … I neglected my routine maintenance of my adult tanks … and noticed that some fish that I classed as difficult had mops loaded with eggs. I have many friends who keep livebearers and they tell me that some of these fish prefer dirty water to produce fry. Another friend who successfully breeds discus .. has about an inch of mulm on the bottom of his breeding tanks.”
So perhaps a little debris in a functioning biological cycle is not a bad thing. A German writer some time ago applauded “clean dirt,” a layer of mulm which he left on the tank bottom while changing water.
“Don’t clean the tanks so often,” suggests Gunnar Asblom. “Dirty water as we think is maybe not bad for the fish. Use a filter and plants such as java moss and you don’t have to clean the tanks, just change the water sometimes, but only 10-20% each time.”
Remember, too, that courting and spawning are variable behaviors, with any number of possible factors triggering them. It’s been well observed that some newly arrived fish go into a spawning frenzy, while others may take a month or more to become adjusted before courting and laying eggs. Sometimes, too, fish simply “take a vacation,” ceasing to spawn for no particular reason and then resuming again “when they feel like it.” –
– G.C.K.A. Newsletter, January 1999 and March 2002
Carbonate Hardness
A term that is readily recognized by most aquarists is “carbonate hardness.” But what, exactly, does it mean?
Carbonate hardness is the result of contact between water (H2O) containing carbon dioxide (CO2) and lime or chalk (CaCO3). Carbon dioxide reduces calcium carbonate to calcium hydrogen carbonate, which imparts carbonate hardness to nearly all fresh waters. In salt lakes, carbonate hardness is partially due to sodium hydrogen carbonate (NaHCO3 ). Many municipal waterworks add chalk or lime to the extremely soft water to prevent corrosion of piping.
The pH value of aquarium water is determined by the ratio of carbonate hardness and carbon dioxide. In most natural waters, the overall hardness consists mostly of cabronate hardness; when it is high, so is pH. When breeding fish, carbonate hardness influences egg maturation, embryo hatching, and the wellbeing of the fry.
Many species have become adjusted to their particular water conditions; under certain conditions, some plants can even utilize carbonate ions as a substitute for CO2. This biogenic declasification can reduce the carbonate hardness of an aquarium over time.
The usual form of nitrate seen in aquaria is nitric acid; this, too can absorb carbonate hardness. If the nitrate content of the water incrases by 22 mg/l, carbonate hardness will be reduced by 1 dKH. In extreme instances, this process can lead to acid fall, a drop in pH so severe that the fish die.
In tanks with good biological filtration, the pH usually remains quite stable, since denitrification daily removes the same amont of nitrate that is present.
Carboante hardness can also be formed in the aquarium. Carbon dioxide fertilizers can dissolve chalk which is present in the substrate or decorations, incresing the hardness. The simpleslt way of increasing the carbonate hardness is to dissolve sodium hydrogen carbonate (NaHCO3 ), more commonly known as bicarbonate of soda, or baking powder. A heaped teaspoon in 100 liters of water increases the carbonate hardness by 3.3 dH. This should not be used in extremely soft water, since bicarbonate of soda contains neither calcium nor magnesium.
Reducing carbonate hardness is most simply accomplished by dilution with distilled or fully desalinated (RO) water, or by filtering the water through peat. Using peat in an aquarium filter for several weeks or more, however, may have the reverse effect, since the material biologically decomposes and releases large amounts of minerals.
References:
Kassebeer, Dr. Gerd. “An Analytical Course for Aquarists,” Part III, Carbonate hardness of the aquarium water.
Today’s Aquarium, April 1986.
— G.C.K.A. Newsletter, May 1998