Welcome to the thread goldmaniac . Soon you will be a zoamaniac.
Well, there is lots of discussion going around regarding the peak conditions for the best of zoa, however, since there is no proven effects for the best of zoos Currently, this thread is based on observations and sharing where one can try and maybe it can work for 1 but not another reefer. so it depends, however, to make a zoa happy, you just need its minimum requirements, to make it bloom like wild grass, its another story.
Yes, goldmaniac , the lights are suitable for the requirement of the zoas. you was saying if you want to place it in a mid-tank level, firstly, how deep is your tank? how deep is your mid-tank level? if a 5feet depth will be incomparrable with a 2feet depth.However, your 2nos of 175W Mh will be able to penetrate roughly at 2feet for maximum penetration. It will make your zoas smile.
From what you said, very long stalks RPE is an indication of them wanting more light, it might be beacuse they are obtained from places of a more penetration from light source as that compared to your tank, condition it and slowly move it higher up till it starts growing sideways.
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Again, not all zoas are fitted at the same position of the tank, this depends on the colour and the source it is from.Some will lose colour when it receive too much light while some may de-colour when it receive too less of a light.
The kelvin (K) of the light is one of the disscussion we had made earlier on, and from my observations, the lower the K, the faster it will grow, but, it will lose its intense colouration, this can be replenish with supplements of iodine and intense Antinics.( a long,long time thou). Improvement wise, its hard to judge as u could mean improvement for the tank overall look ? or for the growth of the corals, anw, a year is good to change thoes bulbs.
Cheers:
Edwan