I was speaking with a lady who has 6 goldfish/koi ponds, a 21 year old convict cichlid who is HUGE, several saltwater tanks, and has done a degree in biology and she told me that doing a water change weekly can often deplete the "good" stuff in the water and though most of the beneficial bacteria grow on the surfaces inside the tank there is something beneficial in the water as well and that instead of doing weekly changes I should reduce it down to 30 percent monthly. It was almost a month ago now that she told me this and I have been refraining from doing the water changes just as she instructed (though I was somewhat critical at first) and to my surprise my ammonia and nitrite levels, which had been a little high despite the tank having been cycled, dropped to zero! So maybe the weekly water change schedule really is unnecessary though I do change my filter cartridge every 3-4 weeks as suggested on the package. I guess it is a matter of trial and error though all ammonia/nitrite levels should be measured frequently to prevent fish loss. However this is only my experience and I am definitely not an expert!
As to the first BOLD section above...
Outdoor ponds are a big difference to indoor tanks. Even ponds that are relatively closed ecosystems (with a rubber or other liner) are not nearly as closed as our aquariums so they benefit from incoming rain (which doesn't really add any nutrients but does change some of the water with heavy rains) and also get air-blown dirt, sand, etc. (which brings in macro nutrients, hardness enhancers, etc.) and all the other stuff that makes them closer to a natural pond than our tanks could ever get close to... but even ponds that get too much rain and not enough normal water will suffer low pH, GH and KH levels and the fish will not do as well since Koi and Goldfish do better in higher pH waters.
IF she's been in the hobby a LONG time... and I'm presuming she has if she has a 21 yr. old convict, she probably is still carrying some old habits into the 21st century... and is simply resisting change.... or using her successes to justify her not wanting to do proper tank/pond maintenance. Especially her comment about partial water changes dilluting the "good stuff"... what good stuff... does she mean dissolved fish poop that is slowly turning the water into diarrhea?
God (or Mother Nature for those who don't like God) does frequent partial water changes on almost ALL of His aquariums (with snow, rain, streams, tides, currents, etc.), that for us to challenge this is ludicrous.
Further, SO MUCH has changed in the past 10-20 years in the hobby, trying to hang on to how things were done in the old days would be akin to saying we should go back to the horse and buggy. Heck, we barely knew how the nitrogen cycle even affected aquaria 20 years ago... even 10 years ago... and it really wasn't until the internet exploded that all of this new information became available to the masses.
As to the 2nd BOLD section above...
You could have been having cycling issues (ammonia and nitrite issues) because you keep throwing your filter cartridge away every few weeks. The overwhelming majority of the nitrifying bacteria live in the filter media... since it's like a drive through of all the food they are looking for, so why not live close to the food supply. When you trash your filter cartridge, you are likely putting your tank into a mini-cycle each time you do and that is probably why you kept getting ammonia/nitrite spikes. See my "Filter Maintenance And Cleaning" blog at
http://goldlenny.blogspot.com/2007/02/notice-this-article-is-very-important.html and there is also a slightly older version of the article here at AC at
http://www.aquariacentral.com/forums/showthread.php?t=108685 and this will further explain how trashing your filter cartridges are affecting your tank's ecology and how you can start properly cleaning them instead and save your money. IF you were doing your partial water changes at the same time you were trashing your filter cartridges, this would likely compound the mini-cycle you kept seeing. IF your tap water is treated with chloramine, there will be a slight amount of ammonia released when the chloramine is broken down by the dechlor product. If you had a fully functioning nitrifying bacteria colony, they would immediately consume this extra ammonia and you would never see it on your tests but if you trashed your filter cartridge, then you have the ammonia from the PWC and the ammonia from the fish and only 10% of the nitrifying bacteria left in the tank (on the glass, top layer of gravel, ornaments, etc.) to deal with all of the ammonia so until they could reproduce enough to handle the ammonia, you would get ammonia readings.
