|
A lot of guys here swear by heavily stocked and fed tilapia ponds/tanks for making green water. The dogma is that the tilapia strain stuff through their gill rakers and, in doing, remove everything but small single cell algae. I don't have a market for tilapia so I use live bearers or older koi and it seems to work OK.
For the three-way thing, if it will run stable for 3-4 weeks I'm pretty happy and that is usually enough to get the fry off to a good start. However, you always need a backup - another green water source somewhere and another pond/tank ready to bloom zooplankton. Eventually, something will crash. I tend to crash them both at once. If the zooplankton numbers start dropping, I crank up the flow to get more algae in there. This will often wash out the green water. Other times, the fry pond will turn green and may even become the best source of green water. Often there is a day or so with low zooplankton numbers as the species composition changes from rotifers or Moina to copepods. When desperate, I go prospecting in other ponds and ditches with a 50 micron net on a long handle.
I see eggs with fungus but don't worry about them and don't use any chemicals or salt. But then, the problem is usually having more than enough fry for the space. Perhaps if you do some counts of fertilized versus non-fertilized eggs under a scope about 12 hours after spawning, and again after 36 hours, you will figure out whether the problem is fungus or fertility. The hard part will be getting a random sample because things tend to come in clumps. With all the commotion and splashing around at spawning, you would think koi would have fewer fertility problems than they do. Most people say to use not more than 2 males to protect the female. If available, I throw in 3 to 5 males but find that only one or two will monopolize most of the action so it's not much different for the female. However, the male doing all the work is seldom the one I want it to be. Also, it's not uncommon to have more fungus problems in a clear-water filtered hatching system than in a pond - probably because the biodiversity in the pond helps keep the fungus in check. I move the spawning mat straight to the pond(s) as soon as the adults have finished doing their thing. Less opportunity for me to screw up.
The little carnivore/cannibal koi can obviously do quite well on a diet of whole fish and seem to have little interest in eating their vegetables. I still want there to be some string algae and phytoplankton flock around so the koi get their vitamin-C. When culling, I toss small tategoi into a pond full of live-bearers (guppy, molly, swordtails, etc.) to get maximum growth from the koi and help keep the live-bearer reproduction in check. Thanks to the koi, the number of live-bearer fry in a pond will stay fairly low until the koi reach about 20 cm. Then, there seems to be a change in nutrition. They stop eating as many live-bearer fry and there is a population explosion. About the same time, the koi will start taking some fresh seaweed when it is offered - just like the adults. Intuition tell me this change is probably very gradual, but it sure seems distinct sometimes.
-steve hopkins
|