Some people say that specifically to avoid constipation issues, but most people will agree it's a bad idea because it sucks the nutrients out of the pellet. Really the cause of expansion/constipation issues with pellets is when people use low quality pellets with lots of wheat. A good pellet should have the first two or three ingredients as whole
fish, not fish meal or wheat. If you have a good quality pellet and you feed correctly it should not cause issues. Aqueon is not the worst, but it's not the best either. For that one I would feed 3-4, spilt up into twice a day feedings and one fast day a week. If you wanted to soak those with vitachem that would be fine though. I wouldn't soak in plain water. I suggest looking for a Omega One Betta Buffet or New Life Spectrum Betta as they're better quality. At this point I would continue fasting for a few more days while you monitor poop in QT.. see below..
Your tank is too cool. He needs to be bumped up between 78-80F, and you should have an in tank thermometer monitoring temps. It should be a stable one temp, and not fluctuate. A good heater should not have a problem with this. What heater are you using?
Would discontinue stress zyme as it messes with ph which is dangerous
Last monday you tested? Even then ammonia was too high. You haven't done a water change in 3 weeks? This is the cause of your problems. Once fully cycled, a tank of this size will need a weekly
water change of 50%, including using a gravel siphon to gently clean the gravel around the plants in bare patches - don't disturb plants. Cycling takes up to 2 months though and during this time you should be testing daily and doing a 50% change any time you see ammonia or nitrite hit .25ppm. In addition to this a weekly 50% change is needed. You also need to use a drops kit and not strips as they are not accurate.
It's probably more than constipation at this point.. it's probably an internal infection, which is why it keeps fluctuating like that.
At this point you need to do a series of several 50% changes over at least the next 3 days to get water quality under control. Test with a drops kit before and after each change and let us know what it is.
As for your betta, I would remove him from the tank entirely and QT him by floating in a 2+ gallon acrylic bowl or critter keeper, filled half full. There I would do alternating 50% and 100% water changes daily along with 1 tsp per gallon epsom salt predissolved. This salt needs to be 100% pure magnesium sulfate with no dyes, perfumes or additives of any kind per the ingredients label. and added slowly over an hour or more to avoid shock. The salt only needs to be readded when you do a water change, and then only as much as water you actually change. In the meantime, monitor poop and let us know what it looks like. He may also need meds.