with the fish tank water its all about the nitrates and nitrites, the fish produce this in the waste they produce, plus all the food you feed the fish and is not eaten gets broken down in the water, most top fertilisers are made from nitrates so fish water makes sense considering it contains everything the plant needs, i dont think you could grow in a fish tank but you could start clones in their, plus the fish tank water works wonders on these plants, i have been feeding one of my clones with just water from the fish tank, and the difference is huge, i got 2 clones growing in soil that was the same size when planted, i fed the one water and bpn and the other fish tank water and bpn, the fish tank fed clone is more than twice the size of the clone watered with regular tap water, so clearly their is something in the water that the plants like, i watered both plants with the same amount of water and nutes so it was as fair as it could be, and clearly the fish tank watered clone is doing a lot better than the regular water clone.
nice update miwa, well done mate everything looks good, my ph of my fish tank water is around 6.8 to 6.9 so the ph is about the same as tap water, my tap water is 7.0 every time i check, plus i dont use any water safe in the tank, this is used to remove chlorine when you do a water change in the tank, but i dont use this as i always let me water stand for at least 24 hours before doing a water change, so i add no chemicals at all, if my fish are ill or got white spot then i add chemicals but i have not had any problems in years with ill fish, so my water is just water, plus its heated as i have tropical fish, i also got many different fish in their so the water is full of crap from these fish, and my plants seem to be liking it.
i spoke to corey about it at bpn as i was unsure of feeding full strength bpn with the tank water, he told me their would be no problems so i used it and my plants showed no problems, just grew a lot quicker than the plants that had not had any fish tank water, even the male plant i give the water to grew like crazy, it was smaller than the female of the same strain but as soon as it had fish tank water it grew like crazy and not its about 4 inches bigger than the fem of the same age