Do you really think you can keep a coral or a reef system for it's normal life expectancy without water changes?
But what about the bacteria, sponges, archea, protists, fungii and phages?
And what about the various Labile and refractory DOCs, particularly the Dissolved Combined Neutral Sugars (DCNS) that promote pathogenic bacterial shifts in the coral holobiont?
(for those who want to learn more about DOC, bacteria and corals start with Forest Rohwer's
Coral Reefs in the Microbial Seas.)
My background:
Started keeping saltwater in '87. Was lucky to bump into two aquarists in '91 who had been keeping saltwater since the mid 70's who mentored me. As I learned it, water changes are needed to reduce all the various waste products, not just nitrates and phosphates. Three givens then were, there is a lot of stuff we can't test for, skimmers only remove hydrophobic stuff and leave hydrophilllic stuff behind and even GAC likely won't grab everything.
In '97 ,a couple years after I started my aquarium maintenenace business I had a very short but seminal conversation with a Dr. Mary Jane Ashby, Ph.D RN, director of an infectious disease department of a local hospital about bacteria. Gist of it was whether a bacteria was "good" or "bad" depended largely on whether it was thriving where it was supposed to be or thriving where it wasn't supposed to be. (I didn't learn of Paul B's posts about bacteria until a few years ago but he's been saying something similar.) Along with what I was seeing in my tanks I shifted from thinking strictly nutrients and nutrient export to holistically about bacteria thinking of a reef system as a single entity. WHile testing for bacteria is just now becoming available (See AquaBiomic's posts) one simple thing I realized then I could do that help significantly at times was use water from a "Healthy" reef system to help a reef system that was having problems. It seemed obvious even then other bacteria than those involved in nitrification and denitrification were a factor in a healthy reef ecosystem.
. . . So religious Waterchanger ppl might say "What about nitrate/Phosphate control? You gotta change your water every 2 weeks!"
In some mild researching, I'm reading how dosing the strain of Blue-Green Phytoplankton OUTCOMPETES nuisance algae and makes for a more balanced tank.
I'm reeeeally starting to think regular waterchanges is dumping good biochemical water down the drain that worked so hard to achieve a balance.
If I can control my NO3 and PO4 thru heavy skimming, dosing phytoplankton .... why would I do a waterchange UNLESS smthg like Calcium or Carbonate or Magnesium was off?
And if I can dose major and minor elements to keep them within range...AND my no3/po4 are in check... why do a waterchange? . . .
There is now huge amounts of research showing to bacteria are critical. It doesn't matter if it's sustainable farming, a healthy natural ecosystem or our own physical and mental health the proper balance of microbial life is essential. Additionally, the research done with nitrogen and phosphates make it clear to me we need to look at totals in a system, organic, inorganic and particulate carbon, organic and inorganic and particulate nitrogen as well as organic and inorganic and particulate phosphorus, not just nitrates and phosphates.
Undoubtidly there are dogmatic individuals who stick to a set recomendation and decry all else as heresy but as a "Religious Water Changer" I like to do weekly water changes. And it's to reduce all waste products not just Nitrate and Phosphate. But weekly is personal prefference not some dictum or dogma. If I had to say, the number I most frequently come across or have been told is probably monthly and the volume percentage varies.
Some years I was better than other years but I've always tried to keep abreast of current research done on reefs and corals. Albiet most of the research has been with benthic algae but it is clear algae and corals have antagonistic roles on a reef system. Both are proactively manipulating the microbial processes around them to benefit themselves and there is some pretty complex biological warfare being conducted on the part of algae. Algae release labile DOC promoting heterotrophic bacteria (oxygen consuming) which includes promoting pathogenic bacteria in the coral holobiont. While coral release labile DOC promoting autotrophic bacteria (oxygen conserving).
(Ironicly the only time researchers could not find any DOC on reefs is when the system had been completely taken over by algae providing enough labile DOC for heterotrophic bacteria to completely consume the refractory portion.)
A system may have lots of coral and a minimum of algae and might be able to go a long time without water changes but without water changes refractory DOC will be building up in a system and we do not know what the consequences are when it gets to 80% or 90%. There will always be some algae releasing the types of labile DOC particularly the DCNS component which from what I've been able to determine is not removed by either activated carbon or skimming and can only be diluted by water changes.
As I see it water changes remove a certain percentage of ALL the microbial life in an ecossytem. Corals and algae exudates will help replenish the bacteria. Depending on what is dominate the bacteria populations will lean towards autotrophic bacteria species (good) or heterotrophic bacteria (bad). I expect someday we'll be able to monitor the holobiont's of the corals in our systems and say "We don't nned a water change" or "We need a water change" but we're not there yet.
And for those who want to dig into more research after reading Rohwer's book here's some links:
Sugar enrichment provides evidence for a role of nitrogen fixation in coral bleaching
https://onlinelibrary.wiley.com/doi/full/10.1111/gcb.13695
Phosphate Deficiency:
Nutrient enrichment can increase the susceptibility of reef corals to bleaching:
http://www.indiaenvironmentportal.org.in/files/file/Nutrient enrichment.pdf
Ultrastructural Biomarkers in Symbiotic Algae Reflect the Availability of Dissolved Inorganic Nutrients and Particulate Food to the Reef Coral Holobiont:
https://www.frontiersin.org/articles/10.3389/fmars.2015.00103/full
Phosphate deficiency promotes coral bleaching and is reflected by the ultrastructure of symbiotic dinoflagellates
https://www.sciencedirect.com/science/article/pii/S0025326X17301601?via=ihub
Effects of phosphate on growth and skeletal density in the scleractinian coral Acropora muricata: A controlled experimental approach
https://www.sciencedirect.com/science/article/pii/S0022098111004588
High phosphate uptake requirements of the scleractinian coral Stylophora pistillata
http://jeb.biologists.org/content/214/16/2749.full
Decadal Environmental Memeory in a Coral.
https://www.academia.edu/11590694/Decadal_environmental_memory_in_a_reef_coral
Indirect effects of algae on coral: algae‐mediated, microbe‐induced coral mortality
Coral seperated from algae with a .02 µm filter die. Treatment with aampicillan prevents death.
https://onlinelibrary.wiley.com/doi/pdf/10.1111/j.1461-0248.2006.00937.x
Influence of coral and algal exudates on microbially mediated reef metabolism.
Coral DOC improves oxygen (autotrophy), algae DOC reduces oxygen (heterotrophy).
https://peerj.com/articles/108/?utm_source=TrendMD&utm_campaign=PeerJ_TrendMD_0&utm_medium=TrendMD
Effects of Coral Reef Benthic Primary Producers on Dissolved Organic Carbon and Microbial Activity
Algae releases significantly more DOC into the water than coral.
https://journals.plos.org/plosone/article?id=10.1371/journal.pone.0027973
Pathologies and mortality rates caused by organic carbon and nutrient stressors in three Caribbean coral species.
Starchs and sugars (doc) caused coral death
http://www.int-res.com/articles/meps2005/294/m294p173.pdf
Microbial ecology: Algae feed a shift on coral reefs
https://www.nature.com/articles/nmicrobiol201661
Coral and macroalgal exudates vary in neutral sugar composition and differentially enrich reef bacterioplankton lineages.
https://www.ncbi.nlm.nih.gov/pubmed/23303369
Sugar enrichment provides evidence for a role of nitrogen fixation in coral bleaching
https://onlinelibrary.wiley.com/doi/full/10.1111/gcb.13695
Elevated ammonium delays the impairment of the coral-dinoflagellate symbiosis during labile carbon pollution
(here's an argument for maintaining heavy fish loads if you're carbon dosing)
https://www.sciencedirect.com/science/article/pii/S0166445X19307192
Excess labile carbon promotes the expression of virulence factors in coral reef bacterioplankton
https://www.nature.com/articles/ismej2017142
Unseen players shape benthic competition on coral reefs.
https://www.ncbi.nlm.nih.gov/pubmed/22944243
Allelochemicals Produced by Brown Macroalgae of the Lobophora Genus Are Active against Coral Larvae and Associated Bacteria, Supporting Pathogenic Shifts to Vibrio Dominance.
https://www.ncbi.nlm.nih.gov/pubmed/27795310
Macroalgae decrease growth and alter microbial community structure of the reef-building coral, Porites astreoides.
https://www.ncbi.nlm.nih.gov/pubmed/22957055
Macroalgal extracts induce bacterial assemblage shifts and sublethal tissue stress in Caribbean corals.
https://www.ncbi.nlm.nih.gov/pubmed/23028648
Biophysical and physiological processes causing oxygen loss from coral reefs.
https://elifesciences.org/articles/49114.pdf
Global microbialization of coral reefs
Rohwer's DDAM Theory Proven
https://www.nature.com/articles/nmicrobiol201642
Because sponges are essential players in the carbon, nitrogen and phosphorus cycle(s) on reefs here's some links to research done with them.
Element cycling on tropical coral reefs.
This is Jasper de Geoij's ground breaking research on reef sponges. (The introduction is in Dutch but the content is in English.)
https://www.rug.nl/research/portal/files/14555035/13completethesis.pdf
Sponge symbionts and the marine P cycle
https://www.pnas.org/content/112/14/4191
Phosphorus sequestration in the form of polyphosphate by microbial symbionts in marine sponges
(Chris Kenndall had a problem with low PO4 and had problems raising it with Neophos. Samples sent off showed phosphorus crystals developing in some of the sponges in his system accounting for at least some of his systems consumption.)
https://www.pnas.org/content/112/14/4381
Differential recycling of coral and algal dissolved organic matter via the sponge loop.
Sponges treat DOC from algae differently than DOC from corals
https://besjournals.onlinelibrary.wiley.com/doi/full/10.1111/1365-2435.12758
Surviving in a Marine Desert The Sponge Loop Retains Resources Within Coral Reefs
Dissolved organic carbon and nitrogen are quickly processed by sponges and released back into the reef food web in hours as carbon and nitrogen rich detritus.
https://www.researchgate.net/publication/279061640_2013_deGoeij_Science_Sponge_loop
Natural Diet of Coral-Excavating Sponges Consists Mainly of Dissolved Organic Carbon (DOC)
https://www.ncbi.nlm.nih.gov/pmc/articles/PMC3934968/
The Role of Marine Sponges in Carbon and Nitrogen Cycles of COral Reefs and Nearshore Environments.
https://search.proquest.com/openvie...9d1e5/1?pq-origsite=gscholar&cbl=18750&diss=y
And since we're discussing favorable and not so favorable bacteria here's a paper looking at how different corals and polyps are influencing the bacteria in the water column.
Aura-biomes are present in the water layer above coral reef benthic macro-organisms
https://www.ncbi.nlm.nih.gov/pubmed/28828261