hello please help me which product should i buy to prevent yellowing? 58. Day

Your plants need more potassium you can use potassium sulfate to correct this issue.

They're getting too much nitrogen and this has caused what's called a "lockout" so the plant can't get at the other nutrients it needs. First - flush your plants which means, for you, running 54L of pH'd water through each pot. In the last liter, add 5ml of BioGrow, 9ml of BioHeaven, and 8ml each of BioBloom and TopMax. Let them dry out. When they're dry, give them some plain pH'd water. When they're dried out from that, give them your normal nutrients BUT do NOT give them more than 5ml of BioGrow and keep the Bio-Grow at this level for the rest of the grow... that is the culprit here... it gives them too much nitrogen. The leaves that have turned yellow will never turn green again. Don't expect them to do that. But you shouldn't see the problem getting worse - in other words, after about a week, you shouldn't see MORE leaves turning yellow. Good luck.

my diary growdiaries.com/diaries/170115-grow-journal-by-kabakcilar

No diary no info what you're using. Can't help with no information mate.

They seem to drop and yellow bottom leaves especially when you have too many nutrients or if your PH was off during a feeding. Defoliate the yellow leaves and switch to water for a while if things continue to worsen. Cal mag does seem to help.

Try cal mag first but could be soil ph issue