Hey grompa, I hate to be the bearer of bad news but from where I sit looking at your blueberry she aint gonna get much bigger, I may be wrong but I dont think so. She looks lovely and healthy so dont worry about the leaves colour...just water and feed with your topmax. What size pot is she in? I have mine in 12L and it is still too small, I really think these blueberrys want 20L. Another observation is that you are using a 250 watt hps with a cooltube right? If so that blueberry needs to be touching the glass almost, my colas wrap around the cooltube getting as close as 1 inch, the plants should be fine if your exhaust is strong enough. The yellowing leaves are fine, I had them too....big time to the point where I thought that it was just eating itself alive...and it was but it put on alot of new shade leaves at 6.5 weeks to my relief. I have been feeding her only topmax for flowering...thats it, I give it every time I water...about 3-4mls / litre I am growing in an organic soil so I let that do all the work, I now know I can buy Plagron royalty mix soil and grow beautiful blueberry buds only having to give topmax and water, it is idiot proof.....Almost
I have done nothing special, just given lots of light to developing buds and let the soil do its thing...seems to work well.
This blueberry loves to be LST'd if you open her up a bit she really will turn into a crown of glory, I have found that they get a bit choked up with bushy leaves...opening it up and removing a few will let the branches ...well branch out
then you can really push her close to the light letting the buds kinda wrap around the tube.
Anyway have a look at how close my girl is to the cooltube...with 250 watts and a cooltube you can get real close, ok my buds are not massive but look at the difference between your girl and mine, and there is 5 days difference in age or so. I would not attempt to grow three plants under 250 watts it is 3 small plants with popcorn buds or one plant with nice colas, I personally want one with colas...the choice is yours.