This wouldnt be a problem to most but.... plants too short

Hey folks.

I have been running a perpetual grow now for maybe 5 months, basically my problem is this, my plants have suddenly halfed in height.
Up until my last two batches my acid and blue cheese plants have been around 75-90 cm, the B.C is always around six inch taller.
I like my plants this height and seem to get better yield from them been slightly taller than some may like, however as i said, my last two batches have been half the height, they dont look to be developing as well, i first put this down to my lights been lower than when i first started, i have since raised my lights back up but now this second batch is just as short. They are all from the same clones.
Now i realise i changed my veg bulb from a 250w hps to a 250w metal halide a while back and i think it would coincide with the time they started shrinking(stretching less).
This is the only thing i can think of, nothing else has changed.
So (sorry for the long lead up) my question is this. Has anybody here changed from HPS to halide bulb for veg and noticed this happen?
I know alot of you like to keep your plants as short as poss, the internodes after vegging with the MH are very close, maybe 1cm apart. where as before with the HPS im guessing about 3-5 cm apart.
Like i say i know alot of folks would be chuffed with such tight internodes but i dont need to keep them so short and would prefer to go back to how they were.
If somebody can confirm my suspicion i will change my bulb back to HPS.

For what its worth.
I grow in coco, using canna coco nutes apart from i use bigbud and overdrive instead of canna boost.
I have 3x 600watts for flowering, two of which are in cooltubes. Plenty of light for the 2m X 1m flower space.
Temps are 79 lights on, 69 lights off.
Plants are from clone and given 3 weeks veg after been repotted in 11ltr pots with a good root system then added to the flower chamber.
I havnt uploaded pics because i dont think you need them to clarify my suspicions.

If anyone has any input please pipe in.
Thanks in advance folks

Corey

P.s i highly recommend the Acid to anyone looking for a resistant, robust plant that can take a beating and tastes amazing.

Cheers for the input guys,

Superstoner, how come you changed back from parabolics? was it Just temp issues? I was going to buy parabolics because of the better light distibution but i came across a thread where folks were saying they spread the light too much and reduce intencity too much for the flowering stage, seem from what your saying though that the opposite happened with you, if they were growing less in height. Either that or ive miss understood your post. My plants could in theory touch the cooltubes, they are only slightly warm, have to say with the cooltube you do lose alot of footprint compared to a standard Open winged reflector but i have twice the coverage in watts and lumens so im not too worried.

Althor, its great when buddys have the same strains with slightly different setups, i have a few friends who use the same strains from the same mothers, one grows with household cfls, he gets 9 inch xmas trees that are pretty amazing considering, another friend uses a 400 hps and he pulled 18oz from 9 over stretched plants (1.4m)in a far too wide an area that had only had two weeks veg under cfl, granted he didnt have the same density buds as mine but jeez, that was his first go. Always nice to smoke the goods and have a sesh compairing each others smokes too, like we need an excuse!!
I agree that a mix has to be a good thing, just getting the right mix thats tricky. Maybe il put my hps back in the veg and get another ballast so i can sling my MH into the flowering chamber, i hear a small amount of the different spectrum can help increase resin and thc production.
Have you noticed any difference in the final dry product between you and your mate using or not using MH.

Happy smokes
Corey