OK. I'll answer paragraph by paragraph to make sure I cover it all... but if you read my above LONG reply, I did discuss spawning in nature. As far as spawning rates, livebearers spawn all the time.... usually regardless of water parameters. Certainly, giving birth and raising fry (for parents that do) is hard on fish so I wouldn't push fish to the extremes but as long as a fish keeper isn't doing things to push fish to extremes, the fish should be fine. This is why we try to match water temperatures and keep other parameters like pH, GH and KH at levels so that a PWC doesn't change their water too much, too fast.... so we don't artificially create spring every week when we do tank maintenance. As far as growth rates, this has been proven scientifically and by hobbyists... doing frequent partial water changes, either weekly, twice a week, daily or hourly, will allow your fish to grow at their maximum natural rate, instead of being stunted by the dirty, polluted tank water with excessive levels of hormones in the water. You can't make the fish grow faster than their natural growth rate unless you are adding some kind of growth hormone or steroid to the tank. You can stunt their growth by underfeeding/overstocking and then not removing the hormones and other pollutants from their dirty tanks.
If they are spawning naturally, then they are probably doing OK. If they are spawning due to your water changes causing them to think it's spring every two weeks, then it may not be OK. As you may or may not know, Angelfish should grow to 6"+ long and 8"+ tall and are BIG fish so they need lots of water volume... at least 35G per fish for long term housing. Breeders will put a mated pair in that size tank but they usually don't stay in that size tank all of their lives... and this is usually once they are full sized adults. Once a fish has reached full size, it won't get stunted, so keeping them in a slightly undersized tank is OK as long as there is proper maintenance being done and the fish has enough swimming room. It's the fry and juvis that absolutely MUST Have adequate sized tanks and water changes and nutrition to allow them to grow to full size so they aren't permanently stunted.
As I and others have said, how much water you need to change out every week and how much tank maintenance is needed is dependent on the overall ecology and bioload of the tank. For example, if you have a single neon tetra in your 120G tank, you could go months without doing a PWC or filter maintenance without a problem. However, if you have two full sized Oscars being fed lots of protein rich foods every day, you would have to do weekly or more frequent tank and filter maintenance to keep their tank from becoming a polluted cess pool. While no two tanks are alike, most newbie fish keepers, unfortunately, overstock and under maintain their tanks which is why more experienced fish keepers strive so hard to try and get them to fix things before they are broken. Some of them hang on to the "If it ain't broke, don't fix it" slogan but once a fish gets stunted, you can't fix it and stunted fish have a much higher rate of illness and a much shorter life span than *normal* sized fish. Most folks have no clue about how long their fish should live which is why I've worked for many years on my blog article about fish lifespans. People think goldfish can live in bowls and only live a few months or years where goldfish should grow to be BIG fish and live 20-40 years or more. Most people think a Betta can live in a small vase and only lives a year or two... but they should be in larger tanks and can live 8-10 years. I could go on and on.
Folks have to decide if they want to listen when someone who is more experienced and knowledgeable tells them that 1+1=2. It always does and always has and it doesn't matter if someone else, somewhere, feels sorry for a them and says 1+1 could equal something other than 2 and gives them partial credit if they answered 3. I regularly see "what works for you may not work for me" type posts. While there are some variables involved in the hobby, as explained above, fish keeping is not an art, it's a science and there are scientific facts that affect almost every phase of our hobby.... not feelings. Folks can feel whatever they want but the scientific facts are exactly that... facts!
opcorn: