This may be a perfectly natural thing that happens but, you have a closed system(nothing natural about that)......all the torn up plants in the pond/filter--all the eggs that are going to decay because they either weren't fertilized or they were attacked by fungus--do and can cause water quality problems...and then if the fish eat the eggs they will poop more--your filters have to be up for the challenge and alot of water gardening folks filters barely handle day to day loads--much less alot of decay in the pond....
Also keep in mind that anytime a spawning happens you do run the risk of injured or even loosing females....
Lawanna
Many naturally occurring earth bottom ponds are closed systems, but their size, under normal circumstances, provides enough bioconversion to handle an event such a fish spawning. You basically have described the problem: insufficient filtration. I make it a matter of policy not to install or engage in a maintenance contract for any lined pond, Garden or Koi, that will not or does not have ample mechanical filtration, bioconversion capabilities and phyto-filtration in combination.
I blame the manufacturers for many ponds being under-equipped. Listing a filter.as being capable of handling, say, a 4000 gallon pond is misleading in the least. Such a blanket claim does not take into account the fish load, number of aquatic plants or the presence of a skimmer, which all factor in.This 4000 gallon rated filter under certain conditions would be hard pressed to adequately handle a pond of 2000 gallons or even less.
It is impossible to over-filter a pond, but very, very easy to under-filter one.
