Macroaalge loss after WC

Hi folks,

I have some weird problem with some of my red macros. The day I do a large (50 %) waterchange the growing tips on some of the reds withering away just over night! The algae are otherwise growing well as long as I dont change water...

Can it has something to do with my tapwater being hard (about 16 dH), and that it gets even harder when I add saltmix to the water (over 20 dH)? That is just my speculation. Another speculation is that the large waterchange removes a lot of something, maybe NO3, and thus starves the growing algae. But would it do so over just one night?... I am all lost.

I must mention though that this happens to a very large extent only to one sort of the red algae, but even Caulerpa taxifolia can loose a leave or two. Racemosa would usually "go sexual" after a waterchange, but came back after the things stabilised (lately I got rid of racemosa because it grew too fast for my taste). Everything else in the tank would look very "sad and tired" after a waterchange too.

Any ideas?

 

So You mean Tom that its the rapid depletion of the inorganic nutrients rather then the sudden shift in water hardness that probably is my issue? In biomass I have only two very small juvenale ocelaris clowns in my 30 litres tank with 44 watts PC-lightning.

 

Allright, the simple advice would then be to do water changes with RO-water, mix salt well, ajust the salinity and temp to the same as the tankwater, and dose back KNO3 and traces after the WC. As long as I dont have RO-water I will try and see how long I can hold it without major waterchanges. Thanks, Tom!