Poor Polyp Extension

[Greg Hiller]

Just in the FWIW category, your tank might actually be more like the natural environment. Anyone that's been diving on a Pacific reef can tell you that during the day polyps are generally not extended much on any Acros. That may be due to fear of predation, or due to higher currents in the natural ocean. Or it may be that in really nutrient rich systems (like most of our) the corals extend their polyps to more effectively absorb the nutrients.

If you are getting good growth, I wouldn't sweat the polyps extension thing, unless you really want them extended. You may be right that it's a chemical warfare thing....more agressive use of carbon, more water changes, or maybe even ozone might help?

 

[scavdog]

I agree with Greg. Here is an excerpt from Advanced Aquarist from 2002 that you may find interesting:

It is a common belief that corals expand at night in order to feed on planktonic prey. However, what is forgotten is that water flow and light levels also play an important role. This paper describes a study conducted in the Red Sea on Favia favus, a massive coral who's polyps open soon after sunset and retract just after dawn. Their results indicate that three factors: flow rate (low= 5 cm/s, medium = 10 cm/s, high = 15 cm/s), light level (low = 40 umol/m/s2, medium = 80 umol/m/s2, high = 120 umol/m/s2) and prey presence (Artemia nauplii), determine the degree of polyp extension at night, but flow rate and light are the main triggers. Tentacle expansion was greatest when water flow was high, light levels were low and prey was present. When no prey was present extension was only 75%. In still water the corals would not extend their tentacles even if light levels and prey density were varied. When light levels are too high (above the light compensation point of 107 +/-24 umol/m/s2) the coral would not expand no matter what the flow was or if prey was present. If no prey was present, and the flow was medium or high, and light was below the light compensation point, then the corals still expanded, indicating that the coral's response to the presence of prey was secondary to water flow and light level. The authors also concluded that since the zooxanthellae density in this species is low, extending the tentacles during the day was probably metabolically more expensive than keeping them closed. They felt that their results may not be applicable to corals with high densities of zooxanthellae and that these corals would be more likely to benefit from expanding during the daytime.

For the aquarist the lesson here is that flow rates need also be taken into consideration when it comes to determining feeding in corals at night. Too low a flow may result in some corals not expanding and hence, not being able to feed. This lack of polyp tentacle extension could be mistakenly interpreted as sign that the coral does not need to or want to feed.

 

[smcnally]

In Calfos "C The Journal", he also explaines that "Great Polyp Extention" can also be a sign of a coral starving.

 

[reefinghabit]

i would check alkalinity if thats no issue. i think maybe tank is to clean as greg stated. corals thrive on nutrients ie phosphate nitrate. even dissolved detritus. fish may be picking on the polyps. you dont however want to encourage phosphate build up. maybe try feeding a good plankton food. strong flow is great for acros especially the long polyp ones.

 

[KenG]

I have had a similar experience. We have a mixed reef and saw poor polyp extension on SPS. Pieces with large polyp extension when purchased shrunk to no extension in my tank. Things did not die, but did not grow fast either.

I added carbon to absorb toxins from the softies. Not real difference in polyp extension, but the water sure looked clearer.

Then two things changed at the same time. I switched from my poor 10K XM bulbs to new 10K AB bulbs which showed markedly whiter light. I also finished my first gallon of Randy's two part and dosed Mg. So I upgraded lights and dosed Mg to a level of ~1600. Since then my SPS polyps have been fully extended and growth is markedly faster.

That is just my experience. I have always had good chaeto growth and have never had a zero nitrate reading (always 10-20) or a TDS reading below 5.

 

[delahunt]

i have similar problems with polyp extension in my display tank, but in my frag tank everything flowers.. cant quite figure it out either

 

[besl]

KenG - interesting commnet on Mg - I thought Mg was suppose to be between 1200 - 1300 - are there ill effects by raising to 1600?

Why I ask... I've read alot on PE looking including what I thought was an excellent thread on RC - Randy H made a comment that he uses IO salt which he has measured the Mg to be around 800. The thread was tied to the topic of PE and the claim was made as to how important Mg was. As I use IO salt, I convinced myself that I had an Mg problem so I immediately ordered 2 different Mg test kits and 2 bottles of Mg - after all, Randy said that IO was only 800. My test kits came and guess what - one measured 1250 and the other measured 1320. Oh well, anyone want to by some Mg or test kits? Meanwhile I join your quest to find why I have poor PE on many sps while very good PE on others.

 

[jebar777]

FLOW


FLOW IS ALWAYS AN ISSUE WITH POLYP EXTENSION





good luck

 

[garyl]

By flow, I'm assuming that you mean strong flow. I do have pretty strong flow (of the linear powerhead sort). I haven't seen any difference in my tank's polyp extension when I change corals from good flow to really strong flow. That being said, there is the possibility that I have the wrong kind of flow. Even though I have the powerheads on a wavemaker, it's still linear flow.

I'm just happy to see from the thread, that I'm not the only one with this problem. If possible, I'd like to hear a little bit more from KenG about keeping his Mg at 1600.

Thanks for all the suggestions, you've given me a lot of food for thought.

Gary