I personally do mine everyday sometimes twice in the QT cups since they are only hold 12 oz of water. But hot water on the tap. You start with one cup (the first and hopefully clean), make sure the temp matches the fish you're going to put in there, condition the water and add the fish. The NEXT cup is the one that betta was in, pour out the water and rinse in hot water on the tap, wait a minute for it to cool, then repeat the process... I don't know where you got 3 days from. Personally I think the betta babies that are jarred need to have clean water everyday.
I read it on bettysplendens.com, the website is given in a sticky about breeding
At about a month I start jarring the largest youngsters and move the rest into a larger grow-out tank. I do full water changes in the jars every other day. When they are 8 weeks old I move them from their quart jars into half-gallon containers, and start doing 100% changes twice a week, removing feces and uneaten food every day with a turkey baster.
I plan on jarring them when they start to show agression, which is at about 8 weeks I read(?)
He/she does 2 full changes a week at that time, and my jars also are about half a gallon (0.39g and 0.52g, I'll fill up the biggest ones first of course)
Have you read about the stunt hormones the fry give off? It can inhibit the growth of your fry.
I'll be doing water changes everyday 100% for the jarred fish, and in the tank 50% everyday, 100% 3 times a week. It'll give them a better start, and keep them healthier. But I'm sure if you suction out the debris on the bottom, it'll be fine. I would just keep an eye on the water perimeters. Make sure you start your cultures now.
But on that same page he/she also says:
"Jarring them early also means not having to worry about fin damage and outbreaks of disease wiping out entire spawns. They also grow much faster once they are jarred."
I'm not saying she's wrong at all! I've been reading and rereading her website over and over again. I was just making sure he knew about the stunt hormone. I think maybe what I've been posting is getting a little mixed in translation, because some of these things seem a bit mixed. I personally won't go 3 days without changing any water in a container. I have to do a 100% everyday or every other day changes in my 1.5 gallons.
There is neither a right nor wrong way to breed and raise them. What ever you need to do, what is available, etc. Everyone does it differently.
If you are planning to show, jar them as early as possible. But remember once they are jarred, their growth will reduce, sometimes a great deal. But if you only plan to keep them as pets, they can be kept in sororities long term as long as they are not disturbed or feel disturbed in any way (including water changing and tank cleaning). Any form of stress will induce aggression.
What I do is move them to growout tanks around 5-10mm. They will unlikely become aggressive at this size compared to moving them after 1cm. In my 40 and 50g tanks, I use water pumps full thrust with an external filter (this reduces current). With this method, I can usually keep them together without any aggression at all for about 3-4 months . . . by which time I can distribute/sell them.
I usually jar the "favorites", using half - one gallon tanks or 2ltr plastic drink bottles. At 1cm this space is adequate . . . and feasible when dealing with hundreds of fry. These fish will grow slower than those in the growouts BUT their fins will be more developed. I often (not always) have 2 tanks/jars for each fish/fry. So when I water change, I just move them to the other container. Or if I run out of jars, I place them in a temporary jar (small) and return them once cleaning is done.
Water changing and jar cleaning highly depends on how I feed them. More feeding = more water changing and cleaning. (my water source is unstable so I need to adjust to water availability). It also depends on food type. Shrimp like foods (daphnia, mosquito larvae, etc can tolerate less water changes compared to wormy foods.) But in general I change 100% and clean every 2 days.
I NEVER immediately reuse containers that have disease. I clean them and leave them dry for a week or so (if possible under direct sun). Hopefully disease will die out without host for 1 week - plus sunlight and no water. (I don't like using chemicals)
Forgot; Rose tails are created by breeding a pair of excessive rays - 8 ray x 8 ray often produces rose. These roses should not be inbred. Pair them to an unrelated 4 ray. AVOID breeding bought rose tails because what ever the breeder claims, you won't know their actual background. Once the X factor gets into your line, it is hard to clean out.