Cat Jockey
Member
I thought about getting an RO water filter, but I also read that if you go that route you will have to supplement with cal/mag.
That is incorrect information. One of the origins of that myth is the fact that a large portion of what is in tap water is Ca, and some Mg. RO got popular and people thought they were putting two and two together to get 4. The only reason you need to add Cal/Mag to a nutrient regiment in a peat/perlite/vermiculite mix (which is what I think you are using - think I saw you added dolomite lime, as well, which I don't understand why ...), is if your base nutrient mfg didn't put enough Ca and Mg in there, like with Botanicrap's Pure Blend Pro line.
Another significant contributor to that myth is the large number of threads, over the years, that involve Ca or Mg deficiencies. In many cases, the reason for those def is the use of tap water and/or improper pH in the rootzone, or a combination thereof.
Tap water in the low to mid 8's like yours can really fuck things up, pH wise, in the rootzone and lead to lockout conditions. It isn't just the ppm and alkalinity, it's the also the buffering capacity of what is actually in that tap water. In addition, just barely watering enough like you are going to have to do with 4 gallon pots and a seedling is a real easy way to get a build up of salts in the rootzone, jacking the pH up and creating lockout conditions. And flushing your rootzone when that does happen is going to be a pain in the ass, 'cause you will have way too much growing medium to roots ratio.
I've never grown an autoflower. But I would be very surprised if an autoflower somehow does not take to repotting well. It is a relatively stress free process, if done properly. Perhaps root growth ends earlier on autoflowers, so it may seem that the roots didn't 'take to the process' and fill out the next pot with explosive root growth.
I just don't buy it, though, and think it Internet Echo Chamber information. Autoflower or not, that pot size and tap pH are going to most likely have a negative impact on the quality and quantity of the chop of yer crop...