Raising and Lowering pH
One can raise or lower pH by adding chemicals. Because ofbuffering, however, the process is difficult to get right. Increasingor decreasing the pH (in a stable way) actually involves changing theKH. The most common approach is to add a buffer (in the previoussection) whose equilibriumholds the pH at the desired value.
Muriatic (hydrochloric) acid can be used to reduce pH. Note thatthe exact quantity needed depends on the water's buffering capacity.In effect, you add enough acid to use up all the buffering capacity.Once this has been done, decreasing the pH is easy. However, it shouldbe noted that the resultant lower-pH water has much less KH bufferingthan it did before, making it more susceptible to pH swings when (for instance)nitrate levels rise. Warning: It goes without saying that acids are
VERY dangerous! Do not use this approach unless you know whatyou are doing, and you should treat the water
BEFORE adding itto the aquarium.
Products such as ``pH-Down'' are often based on a phosphoric acid buffer.Phosphoric acid tends to keep the pH at roughly 6.5, depending onhow much you use.Unfortunately, use of phosphoric acid has the
BIG sideeffect of raising the phosphate level in your tank, stimulating algaegrowth. It is difficult to control algae growth in a tank withelevated phosphate levels.The only advantage over hydrochloric acid is that pH will be somewhatbetter buffered at its lower value.
One safe way to lower pH
WITHOUT adjusting KH is to bubbleCO2 (carbon dioxide) through the tank. The CO2 dissolves in water, andsome of it forms carbonic acid. The formation of acid lowers the pH.Of course, in order for this approach to be practical, a steady sourceof CO2 bubbles (e.g. a CO2 tank) is needed to hold the pH inplace. As soon as the CO2 is gone, the pH bounces back to its previousvalue. The high cost of a CO2 injection system precludes its use as apH lowering technique in most aquariums (though see the
PLANT FAQ for inexpensive do-it-yourselfalternatives). CO2 injection systemsare highly popular in heavily-planted tanks, because the additional CO2stimulates plant growth.
Softening Your Water (i.e., lowering GH)
Some fish (e.g., discus, cardinal tetras, etc.) prefer soft water.Although they can survive in harder water, they are unlikely tobreed in it. Thus, you may feel compelled to soften your water despite thehassle involved in doing so.
Typical home water softeners soften water using a technique knownas ``ion exchange''. That is, they remove calcium and magnesium ions byreplacing them with sodium ions. Although this does technically makewater softer, most fish won't notice the difference. That is, fishthat prefer soft water don't like sodium either, and for them suchwater softeners don't help at all. Thus, home water softeners are notan appropriate way to soften water for aquarium use.
Fish stores also market ``water softening pillows''. They use thesame ion-exchange principle. One ``recharges'' the pillow by soaking itin a salt water solution, then places it in the tank where the sodiumions are released into the water and replaced by calcium and magnesiumions. After a few hours or days, the pillow (along with the calciumand magnesium) are removed, and the pillow recharged. The pillowssold in stores are too small to work well in practice, and shouldn'tbe used for the same reason cited above.
Peat moss softens water and reduces its hardness (GH). The mosteffective way to soften water via peat is to aerate water for 1-2weeks in a bucket containing peat moss. For example, get a (plastic)bucket of the appropriate size. Then, get a large quantity of peat(a gallon or more), boil it (so that it sinks), stuff it in a pillowcase, and place it in the water bucket. Use an air pump to aerateit. In 1-2 weeks, the water will be softer and more acidic. Use thisaged water when making partial water changes on your tank.
Peat can be bought at pet shops, but it is expensive. It is muchmore cost-effective to buy it in bulk at a local gardening shop. Readlabels carefully! You don't want to use peat containing fertilizers orother additives.
Although some folks place peat in the filters of their tanks, thetechnique has a number of drawbacks. First, peat clogs easily, soadding peat isn't always effective. Second, peat can be messy and maycloud the water in your tank. Third, the exact quantity of peatneeded to effectively soften your water is difficult to estimate.Using the wrong amount results in the wrong water chemistry. Finally,when doing water changes, your tank's chemistry changes when new wateris added (it has the wrong properties). Over the next few days, thechemistry changes as the peat takes effect. Using aged water helpsensure that the chemistry of your tank doesn't fluctuate while doingwater changes.
Hard water can also be softened by diluting it with distilled wateror R/O water. R/O (reverse-osmosis) water is purified water made by aR/O unit. Unfortunately, R/O units are too expensive ($100-$500) formost hobbyists. R/O water can also be purchased at some fish stores,but for most folks the expense and hassle are not worth it. The sameapplies to distilled water purchased at grocery stores.
