i think jin' would have a better opinion
sorry mo, i'm trying to help i really am, in my opinion, your plant is more mature than you think, just because she's had a slow start, and taken a long time to get her that big, i believe she could handle a decent feed regime....certain nutrients are high level ppm to start with, i know that when cyco is mixed to full strength it is always over 1000 ppm, but remembering that not all of that is unusable salts, some will break down and turn into food, i just think with the added stress that she has gone under, she is finding it hard to uptake the nutriens, but she is only going up from here, the plant is starting to self sustain, and her leaves will start to show problems earlier. you will know if you've given her too much food, she will perk right up, and the tips will point straight up, find that balance and you will be fine, maybe bring food up to around 600-700, see her reaction, thats not enough to do damage, and will give you an idea, under the light for 3hrs on that ppm will show you results, if you arent seeing results in that time, then up the food...... my opinion, this is different to my hydro, so maybe ask jin, see if he agrees