When the fry are swimming horizontally it is time for action.
These are the same words that we used to begin talking about feeding the fry. That's because at the same time the fish are needing to be fed, the changing water quality needs to be addressed also.
"But the babies are so tiny," you say. True enough, but the fish still create waste. At some point in the process you will need to begin water changes and other tank maintenance chores (or maintenance opportunities if you need to use a different phrase).
If you have chosen to use the half filled 10 gallon aquarium for the spawning environment the first couple of water changes are very easy. If you are using our recommendations for feeding the foods will be live and some of them will live for days in the water...vinegar eels and paramecium for example. Because the food lives in the water it will not decay if uneaten. Of course when it dies or is consumed it enters into the nitrogen cycle and becomes a future water change, but live food helps to mitigate a rapid build up of nitrogenous wastes.
Essentially we change the water for the first week by adding water to the tank. We add one inch of water each day when we start to feed. When the water fills the tank we begin a more traditional approach to changing water.
Granted, one inch additions do not add up to a massive water change but between the live food approach, the one inch additions and an active sponge filter the water stays in great shape.
Did we forget to mention the sponge filter? In the page regarding the spawning environment we talked about putting a sponge filter into the tank with the pair. That active sponge filter is a good biological device that can now provide biological filtration for the growing fry. The bacterial colonies will grow with the increasing bio-mass of the spawn. You can keep the same sponge filter with the fry until they are moved into a larger grow out tank at about a month in age.
Sometime around two weeks of age the bottom of the tank will become fairly "interesting." We're trying to use sensitive language here, but "interesting" could also be termed "disgusting." You can take you pick, but the way we approach the solution will be the same.
When the bottom of the tank looks like the floor under the refrigerator (you didn't think anyone else knew about that did you?) you need to remove the mulm/detritus. The detritus will continue to decay and add nitrogenous waste to the water column. Some of the effects of the waste can be mitigated through the water change process, but the growing fish and their heavy feeding will be creating a situation where the environment will be increasingly less desirable. A some point it will become impossible (or perhaps impractical would be a better term) to change the water often enough or in great enough quantities to keep the nitrate level in check unless you remove the detritus.
We use a piece of rigid airline about one foot long which is attached to a length of airline tubing to siphon the detritus from the bottom of the tank. We direct the siphoned material into a white bucket. We use a white bucket so that the inevitable sucked up fry will be able to be seen and rescued from the bucket. If you want to try a black bucket, be our quest. We have used a dark bucket before...it was a very "special" experience (substitute "stupid" if you wish...it's how we felt at the time).
We use the siphon about once a week beginning at about the end of the second week post free swimming (remember that we are adding an inch of water a day for the first 5-6 days). Because we move the fry into a new tank at one month, we only need to do the siphon job 2 or perhaps 3 times while the fish are in the 10 gallon spawning environment. At one month the fry will be moved into a 20 gallon tank and a week will pass before we need to siphon again. At the time the fish are about 5 weeks old, they are large enough that siphoning them into the suction tube is pretty easy to avoid. We change to a large tube to speed up the process.
The new tube is a 3/8 inch diameter pipe with hose. The end of the rigid tubing is covered with a small piece of nylon stocking attacked with a rubber band. The stocking material lets most of the detritus through and still allows you to blink your eyes or turn you head without the fear of sucking up one of the fry.
Back to that first week...once the tank has been filled through the series of once inch water additions regular water changes are undertaken. These changes are separate from the siphon duties and are done daily. We change 15% of the water every day on spawns of 100 or less fish and about 25% per day on larger spawns. We have a tool for this process also, because like you, we didn't think we would be able to do the changes.
We use a piece of rigid airline tubing (we really do like this stuff) and bend it carefully over a heat source into a "U" shape. One end goes into the tank and the other is attached to a flexible airline tube that is long enough to go into a bucket on the floor. We cut the end of the tube that goes into the aquarium to the length we need siphon from the tank (either 15% or 25ish%). The end of the tube that is in the tank is covered with more nylon stocking material to keep the fry from being sucked up and out. We begin the siphon and walk away. This a slow process, but the effortlessness is worth the time.
We replace the drawn water by placing a plastic pitcher with water onto the top of the tank and using one of the detritus removal siphon tubes, start a siphon back into the tank. This slow process of replacing the water reduces the shock of the water change to something on the order of insignificant from negative impacts. Of course the water you would want to use as replacement water should be approximately the same temperature, TDS (Total Dissolved Solids) and pH as the water in the tank. Our water is very stable from the tap so this is easy for us. If you need to treat your water to change it's basic qualities you should do that in large quantities prior to setting the fish up for spawning. You should think in terms of a 30 gallon batch...the bigger the batch, the less chance you would have changing the environment too quickly. I know that when you read the 30g suggestion you you thought "what would the family think?" At this point in the process they probably think you're a little nutz...so why stop now?
All fish fry are somewhat fragile during their first few weeks. Creating a food rich, clean water, constant temperature and stable environment is important to high survival rates in the spawn. In the natural environment, long before the fry are large enough to catch the eye of most predators, it is the lack of or the instability of the various components that kills the bulk of the newly hatched fry.
Once the fry are transferred into the 20 gallon grow-out tank, the care of the water is pretty much like all fish. We continue the daily 25% minimum water changes until the sub-adults are jarred. If the spawn is still larger than 100 fish we will begin 50% water changes. Once you jar the fish you are again faced with some interesting challenges.
Good notes help.