Large water changes have large effects on the aquarium microbiome

[EMeyer]

Hi everyone,

Since some of you have had your aquariums' microbiomes tested more than once now, you have probably noticed differences and wondered why. 

While we're thinking about changes in the microbiome I wanted to remind you of this classic paper on the effects of large water changes in aquariums. The authors found that

• Microbial diversity increased substantially following a large water change (90%)
• The groups enriched after a water change include both Cenarchaeaceae (ammonia oxidizing Archaea) and Vibrionaceae (a group with lots of pathogens). (These specific effects probably depend on what community you start with before the change)
• The authors emphasize that microbial communities are destabilized by disturbances, leads to a succession effects like those that happen after clear cutting a forest (just much more quickly!)

This is why I've always advised clients to sample before doing any of their daily maintenance. But its worth thinking about more broadly. Even if you didnt change anything in your system between sample 1 and sample 2, even normal maintenance events may affect the community for a while. 

The authors suggest the changes are unlikely to affect the health of the inhabitants, but I'm not so ready to assume that tripling the ammonia oxidizing microbes and tripling Vibrio are neutral effects. They just werent measured here. 

And the study makes me wonder about automated low volume water changes vs infrequent large ones.  I didnt capture that info in the survey. I wonder, for those of you who were tested, what are your water change practices and how do those affect the stability of your microbiomes?

[SuncrestReef]

I've been doing automated daily water changes in my tank for almost 2 years.  I have varied the amount, from 1.5 gallons to 3 gallons daily depending on tank conditions.  I only occasionally do large water changes, typically every 6 months when I'm doing major sump maintenance to clean all my pumps, skimmer, and UV.  I always keep a minimum of 30 gallons of new saltwater on hand just in case I need to do a larger change.

[EMeyer]

So not only are your parameters rock solid between the two samples, there werent even any large water changes. This makes the changes in several major families in your tank even more interesting.

Although theyre unexpected I am inclined to believe them, and only wonder why. For comparison here are some of the changes during establishment of an experimental tank with live rock. The samples are about a week apart. So at least for some tanks, microbiomes remain relatively stable and recognizably the same over this time scale. (None of which is to say this microbiome shown is in better health than yours; in fact yours is more similar to the typical community than this one). Even during the dynamic early days of establishing a new tank.

And a figure I've shown before, demonstrating that duplicate samples taken at the same time (A1 and A2) produce nearly identical results. So I think its unlikely the differences result from random errors in estimating the community. 

 So I'm stumped what caused the change but inclined to believe it is a real change in those families... 

You havent changed anything, and your measured parameters are rock solid. Have you seen any differences in the livestock? (I'm thinking of subtle unreported things like more or less algae on the glass, etc) Its a puzzle... So much for the water change idea in your case, huh!

[NateDawg]

Could changing light fixtures be cause of microbe change?

[SuncrestReef]

27 minutes ago, EMeyer said:

So not only are your parameters rock solid between the two samples, there werent even any large water changes. This makes the changes in several major families in your tank even more interesting.

Although theyre unexpected I am inclined to believe them, and only wonder why. For comparison here are some of the changes during establishment of an experimental tank with live rock. The samples are about a week apart. So at least for some tanks, microbiomes remain relatively stable and recognizably the same over this time scale. (None of which is to say this microbiome shown is in better health than yours; in fact yours is more similar to the typical community than this one). Even during the dynamic early days of establishing a new tank.

And a figure I've shown before, demonstrating that duplicate samples taken at the same time (A1 and A2) produce nearly identical results. So I think its unlikely the differences result from random errors in estimating the community. 

 So I'm stumped what caused the change but inclined to believe it is a real change in those families... 

You havent changed anything, and your measured parameters are rock solid. Have you seen any differences in the livestock? (I'm thinking of subtle unreported things like more or less algae on the glass, etc) Its a puzzle... So much for the water change idea in your case, huh!

I went back and checked my logs.  I sent you the water sample on October 9th.  On October 15th I started dosing Flux RX (Fluconazole) to treat a bryopsis problem and turned off the auto water changes.  Then I did a 20% water change on October 29th.  I just wanted to confirm the sample was taken before the water change.