Question on water change

[MoonShadows]

Not sure of the cause and effect of this, but the only time I did a water change of about 20% because I thought "it was time", was when shortly afterwards I had a terrible outbreak of green water. Did my water change upset the balance? I haven't done a water change since.

I also stopped cleaning my filter on a 2 week schedule as recommended by the manufacturer, and my water has never been clearer. The outside of the filter (a submersible) looks like something that has been at the bottom of a lake for years, and I imagine the inside is full of all kinds of (good) stuff, but the flow does not seem to have diminished. I figure why fix what isn't broken. Eventually, I will clean it, but I don't see the need to do it now. I am assuming that the 2 week schedule is not crucial since my filter is in my 425 gallon pond, but is rated for a pond up to 2000 gallons (manufacturer's spec) with a flow rate of 941 gph.

 

[IPA]

@MoonShadows , I have been reading recently about fish waste and the bio-load on filtration. I think the real reason to clean filters is to remove the eventual buildup of unprocessed solid waste which is not broken down by the nitrifying bacteria. Only until the ammonia is released is it then processed by NB, otherwise it is fungus and other bacteria, and protozoans which can become harmful to fish if populations get out of control, meaning the fish's natural defense keep it at bay when they are healthy. What probably happens is a trauma event weakens the fish's immunity and the bacteria, fungus and parasites in such high populations can then gain a foothold against the fish.

 

[Meyer Jordan]

What probably happens is a trauma event weakens the fish's immunity and the bacteria, fungus and parasites in such high populations can then gain a foothold against the fish.

You are absolutely right by stating that a fish's weakened immune system is the cause of fish health issues. However, the assumption that high populations of pathogens increase these chances of infection are not founded in fact, especially in a eco-pond where diversity of organisms is encouraged, even welcomed, This sets up Nature's checks and balances, predator-prey scenario that would inhibit any population explosion of any particular micro-organism, even pathogenic. Fish, being exposed to several pathogenic agents develop the means to maintain a healthy functioning immune system of which the slime coat is an integral part.
In DKPs fish will also maintain a level of health, but only because they are not exposed to these same pathogens on a continual basis. This results in an immune system that is less than fully functional....the old 'Use it or Lose it' adage. Thus when exposed to these pathogenic agents they are more prone to infection, especially in the Spring.
All of this is not to say that overall water quality does not also play a major role.
The mulm that accumulates in biofilters is a complex assortment of many, many different species of organisms, not all microscopic. This mulm is a genesis point of the total wide diversity that Nature provides and should only be removed when it affects nitrification.
A fact not widely known is that nitrifying bacteria comprise only a small percentage (5% of less) of any biofilm extant in a pond and may not be present in a biofilter at all after a pond is established having been replaced by archaea.