| Water Changes |
Here is another topic that has many schools of thought and no easy answer.
Some people take the tact of minimal water changes, believing that aged reef tank water takes on a chemistry that should not be disturbed. This is often more a pride thing than anything else. It feels good to be able to maintain an ecosystem for extended periods of time with minimal influences from the external world. The end tank result is less important to the hobbyist than how they got that result. When I have run a tank without water changes, the tank seems to do OK for a period of time and then starts to decline. This decline is characterized by the corals taking on a less robust look. LPS corals tend to not open as fully for instance. This change is gradual over time and not immediately obvious, due possibly to the fact that the corals are consuming some of the elements in the water. Although there are trace element replacement additives you can add to the tank, they only replace the major elements that are known to be consumed in the reef tank in quantity such as strontium or magnesium. There is no doubt that other traced elements available in newly mixed seawater are also consumed to some extent and we do not yet know what those are, so they are not replaced. The only way to replace those elements currently is through replacement of some portion of the tank water.
Other people take the tact that massive water changes should be made to dilute any possible pollution in the tank. Large water exchange regimens can get somewhat complex. These often revolve around premixing large quantities of water, heating it up to the correct temperature, aerating it to increase its oxygen content, shutting down the circulation system, draining a significant portion of the tank water and then replacing it with the new water without exposing the corals for too long of time to the air. The obvious question here is why the hobbyist must dilute pollution in their tank, since a properly balanced system should not have pollution per se. Large water changes (around 25% of tank volume) can be helpful as a remedy to help correct an out of control situation in the tank, but depending on it to maintain basic water parameters over time usually indicates that the tank is not properly setup. The usual reason for large water changes is to try to dilute elevated nitrate levels, but controlling nitrates with water changes is a losing proposition, as you are only addressing the symptom of the problem and not treating the problem itself, which is insufficient nitrate processing within the tank. A properly setup reef tank should have zero or near zero nitrates with or without significant water changes. Large water changes cannot easily be made without subjecting the tank inhabitants to at least some amount of stress via temperature change, salinity change or other water chemistry change. Also, large water changes can tend to undo water chemistry alterations that have been made intentionally, such as increased Alkalinity levels. It tends to go against one of the primary rules of reef keeping which is to maintain a stable environment.
As with most extreme views, the best course of action for most hobbyist’s lies somewhere in between these two viewpoints. Small frequent water changes of 5-10% or so seem to provide good results on several fronts.
| This size of water change can usually be made with water volume available in the sump, thereby removing the problem of exposing the corals to the air or requiring circulation systems to be shut down. |
| The percentage is small enough that it cannot significantly alter the water parameters even if the chemistry, salinity or temperature match is off somewhat. |
| This quantity of exchange does not require the replacement water to undergo extensive premixing, aeration or even heating if the water addition is made slowly. |
My 20 gallon desk tank which keeps Softies, LPS and clams receives a 1 gallon water change a week which equates to a 5% change. This tank receives no other additives and this 5% water change provides all that the corals appear to need. The seawater is mixed in a 1 gallon jug by simply adding the salt and shaking it, checking salinity level and then letting sit for a short period.
My old 70 gallon tank which housed all types of specimens, but was predominately an SPS coral tank, got a 1 to 3 gallon water change a week which equates to about a 1.5% to 4% water change. This tank also got other supplements to maintain high calcium and alkalinity levels which water changes alone could not provide. The same basic approach to mixing the water is taken as with the 20. Just multiply the process by a jug or two more.
Obviously, very large tanks may require a slightly more complex process based simply on the volume of water that must be handled. In that case, a clean trash can (reserved for this purpose) or similar can be pressed into service to provide an adequate mixing container volume.
My 225 currently gets about 25 gallons changed each week. I utilize a large plastic tub from the hardware store. I keep a heater and small power head in it. I add 25 gallons of RO/DI water and turn the heater and power head on. I then dump in the salt and let it run overnight or at least until the water temp comes up to that of the tank which usually takes 4-6 hours. I do a quick check on the salinity and adjust if necessary. I then turn off the pump and heater and siphon the contents into the sump of the tank.
Further Reading:
To
Change or Not To Change Water — That Is The Question
By Terry Siegel
