Ammonia and nitrite--toxic metabolites that can accumulate in recirculating aquarium systems are probably responsible for more fish mortality than anything else including parasitic infestations. We tend to see concentrations of these compounds at their highest during the initial "cycling" period. During this time, there are few or no nitrifying bacteria to convert these poisons into less harmful nitrate. The result is an ammonia spike, then a spike in nitrites. After some lag time, the nitrifiers finally get their act together and both ammonia and nitrite drop in a fairly predictable manner. Then, time to buy some fish! And no need to keep any more of that TurboStart around, right?
Well, maybe there is! In fact, it's a rather good idea to keep a bottle on hand just in case.
Just in case what?
An aquarist's work is never truly done. Aquaria are dynamic and living. An aquarium keeper cannot just walk away from their creation, like a sculptor, and declare it finished. Rather, the keeper must feed, clean, feed and clean. Once in a while, they might add a new fish or coral. Once in a while, a fish or a coral might die. But if one thing is for certain, it is that an aquarist is dealing with a work in eternal progress. Their chances of success often hinge on their ability to intervene quickly and decisively in the face of each "ecological" catastrophe and bring the system back to some perceived state of equilibrium or normality. To be truly prepared for the worst, one certainly must be ready to fend off the next visit from the worst of all menaces: ammonia.
Yes, ammonia can return to rear its ugly head at any time. Maybe the worst of times, like right after you just introduced a very delicate, hard-to-get flasher wrasse and a rare, pricey SPS coral.
How can this happen, after your biofilter has become so established?
Actually, all sorts of events can throw off your system's capacity for nitrification. It may be that some seemingly minor changes in water chemistry negatively impacted the bacterial colony, interrupting their ability to metabolize ammonia and/or nitrite at the typical pace. A power outage could interrupt flow through a trickle filter, suffocating and killing off much of the colony. Maybe you just added some animals or increased your feeding, and the colony did not increase fast enough to compensate for the increased bioload. It could be that something big died and you were unable to find its remains as they decomposed in the tank. No matter the cause of the spike, you surely will begin to lose livestock soon if action isn't taken immediately! Massive water changes are one sure way to dilute the ammonia fast. However, since this doesn't necessarily remedy the cause (say, there's still a big, dead, sand-sifting sea cucumber somewhere under your hardscape), the ammonia could return with a vengeance in very short time. Not to mention that this type of aggressive water exchange can be stressful for both fish and invertebrates.
In the above scenario, a much easier, less expensive and far less traumatic means of mitigating the spike is to take a short-term, then long-term approach to solving the problem. The short-term solution is to neutralize the existing ammonia threat instantly and safely by adding Fritz A.C.C.R. Liquid (yet another product that is good to have "just sitting around"). The long-term solution (you guessed it!) is to beef up the bacterial colony by generously adding TurboStart. Sure, eventually the colony would increase in size on its own, but this act of intervention speeds up the process, potentially sparing your animals' lives! With so many things that can go wrong in a reef tank, and with so much to lose, it's easy to imagine why someone would want to be ready to add TurboStart to their system in a moment's notice.