Zoas/Pallys Reaching observation

[Sundevil_B]

So I just wanted to share an observation. Obviously anecdotal, however I had noticed that some of my zoas and pallys were "reaching" or stretching. I looked for solutions and a lot of forums point to either light or flow. My light I thought was adequate so I concentrated on flow. My pallys were the worst offender really reaching at least 3cm so I moved them to higher flow but lower light. In my tank currently there isn't a high flow high light area.... Regardless they did a little better but still were reaching. Another Zoa was also reaching a little but nothing crazy.

 

This past weekend I managed to do a larger water change of 40% after neglecting for a couple of weeks. It's a pico 5gal so only 2 gallons. However after the water change both the zoas and pallys retracted a lot! the zoas actually got knocked half way down the tank after the water change as well by one of the snails or hermit but still was flat against the frag substrate as apposed to reaching like before. Similarly the pallys which were reaching before actually shrunk down to "normal" of 1cm off frag substrate. I did move them back up to their previous lower flow location during the water change but they were there before and were still reaching.

 

I've just been using Test strips to make sure everything isn't completely out of whack but obviously the granularity isn't great. I know the Nitrates were under 20 ppm before water change.... 

[Sundevil_B]

adding pics for reference. This is of them stretching even at the top of the tank. They looked like that since I got them from LFS.

 

And here is them a couple of days after the water change. much shorter. similar water flow as the pic above.