Reactions to water changes

[G-money]

Hi Randy,

I was going to shoot this one at Eric, but I think you may actually be the man. Hopefully this is within your realm of interest....

I have noticed that many of my hard corals (especially Acros and Montis) pull their polyps in after a water change - sometimes for 24 hours. Curiously, my gorgonians, star polyps, and clams stay open as normal. I change about 1/3 of my 90 gallon tank every month. I bring the fresh mix up to salinity over 24 hours and then mix it at salinity for at least 48 hours quite vigorously. It is all completely dissolved and the solution is crystal clear and at temperature before added to the sump to be sent up to the tank. The parameters of the new water are completely acceptable (ph, Alk, Ca, NH, NO2, NO3, PO4)

Is this some sort of reaction to ion "bombardement"? I know I am adding a solution with comparitively less dissolved organic material than the "dirty" water from the tank. Would this cause a reaction due to an increase in the ionic : organic compound ratio? I have heard of people seeing this reaction after using "quick-mixed" water, but 48 hours should be enough, eh? I use IO exclusively.

TIA...

[Randy Holmes-Farley]

Graham:

I guess you'll have to send it to Eric too, as I don't have a very good answer.

A few possibilities:

1. The new water has something dissolved in it that is irritating some of the corals. FWIW, there is more in salt mixes (and fresh mixed salt water) than is present in tanks using that salt. All one has to do is look at studies like Craig's and Ron's to see that some ions are very high in freshly mixed water, but don't really end up in tanks using them (at least not for long). One or more of these ions may be irritating to corals at the greatly elevated levels found in some salt mixes.

2. Organics (either as DOM or POM) may be an issue, as you suggested.

3. The fresh salt water may provide some important nutrients (especially metals) that drive rapid growth of microorganisms that irritate corals themselves or through their waste products.

4. The simple act of doing a 30% water change (even with identical water) may stir up crud in the tank that, even if not noticed by you, may irritate the corals. All it might take is a single coral to be irritated that slimes, and the slime irritates other corals......

Anyway, I don't have a good answer, just some possibilities.

[G-money]

Thanks for your input, Randy!