Purpose of water changes

Hi everyone

I've been reading up on Discus keeping (but it could be applied elsewhere i guess), and while most of it seemed pretty straight forward (good food, clean water, medication), i was left with 1 question.

Why do water changes?

The generic, easily available answer is to maintain perfect water quality, but finding good examples of what we're trying to remove/dilute isn't as specific.

Basic ideas that are mentioned are:
1. Removal of nitrogenous compounds (ammonia, nitrite, nitrate)
2. Removing decaying organic matter (left over food, fish poop etc) which can result in other nutrient spikes
3. Restore missing trace elements and minerals that get used up
4. Bacterial blooms

Now, the Triton method for Saltwater got me thinking. To provide solutions for the points above, they would be:
1. Duckweed/floating plants/hang on back "refugium"/riparium for nutrient export
2. Same as point 1, but with a substrate vac for particulate matter
3. Adding an appropriate (confirmed with testing) amount of a gH/kH booster to tank when topping up.
4. Excessive amount of biological media and an inline UV filter

Is there anything I'm missing?

Cheers,
Kean

 

I've not kept discus myself (yet), but have mates that have in the past - some with the minimal bare-bottom and heavily filtered approach, others with the heavily planted route, and some inbetween.
Varying success. From my own research, starting out with good stock, at the right age and health, is the first important step.

Setup wise, doing it myself and with no breeding intentions, I'd probably go the 'middle ground route' of nice hardscape, SOME plants, and good filtration - @Nico Hamman has that locked down with an impressive tank.
I saw in an interview with the guy running Jack Wattley Discus these days (I forget his name) that he has, at his own home, a heavily planted discus tank that he does water changes once a week on - and not huge amounts.
Goes against half the internet, and yet the guy has been breeding and keeping them for literal decades.

One thing I don't quite understand - these fish often come from regions with ultra low TDS- so, few minerals. Then I read about 'redox' and its importance. Same story for rams, but they come from similarly low mineral regions, and yet grow up healthy?
There is a lot of good reading on this site that I have linked previously for anyone who has the time: http://www.americanaquariumproducts.com/Basic_Aquarium_Principles.html

I get the impression one needs to be properly experienced in the hobby before going near discus, but have seen success with people just getting the basics right.

 

Apologies, I should have mentioned that top up would have been done with RO water. Similar to maintaining salinity in a saltwater tank. I know some people tried to raise discus in straight RO water, but found that they never did as well as those who used a tap water /RO water mix, which would imply that the fish need those minerals for health. This is probably due to osmotic regulation rather than taking on those minerals for growth, so this might be an unnecessary step unless the plant mass just sucks up all of it.

I've spent many an hour listening and watching that channel, just trying to funnel as much knowledge into my noggin as I can. His heavily planted home tank holds adults as far as i know, which do not need as rigorous a maintenance schedule due to their immune systems being strong enough to cope. The juveniles are the tricky ones.

With regards to Redox, that webpage got super technical without actually mentioning what a good balance would be...at the end of one of the reference pages it basically just came down to "Use a TDS meter". Maybe i need to read some more...

Thanks for the detailed reply Maria

Removal of nitrogenous compounds (ammonia, nitrite, nitrate)
I was under the impression that there is still a trace amount of ammonia and nitrite in the water, even in a fully cycled aquarium? On the plants front, this makes sense. By having a hang on back riparium in combination with duckweed it should be possible to have a significantly larger plant load than fish load, but it would be situation dependent.

Restore missing trace elements and minerals that get used up
Apologies, forgot to mention that top ups would be done with RO water, though having a large plant load might also drop this value too. I understand your concern with additives, but the relatively small amount being added to maintain water TDS shouldn't be too risky (in theory, never tried it)

 

One thing that I have learnt in my 30 plus years of keeping fish both fresh and marine, is that there are always more than one way to do things and successfully too.

 

When I was new to the hobby some years back there was a saying - "Freshwater fish love fresh water". Now I feel that keeping the system stable is more important. Its a closed system essentially - nothing gets in our out unless we put it there. As has been said everyone needs to do what works best for them. And the requirements change depending on fish species, fish numbers, type of setup and filters you are running etc. Just be aware that small regular water changes keep things more stable than large infrequent water changes.

 

Here's another though. A friend of mine doses about 2ml of vodka per day in his salt water aquarium. This apparently boosts the bacteria in your system to process ammonia, nitrates and nitrites quicker. I have not researched it, but I have tried it on my fresh water aquarium. It seemed to help a bit.

 

So, i asked almost exactly the same question over at the SimplyDiscus forum. Seems that, for the purpose of raising juvenile discus, the issue isn't the water quality but rather managing the biomass/bioload in the tank.

The main task is actually to scrub down all panels to lift this biomass off the surface, and the water change is just the most effective way of getting it out of the system. This biomass can be the cause of toxic compounds and various pathogens that will not be picked up by the test kits.

I forgot to include the part about the UV steriliser, so going to check with them on that now

 

Interesting thread

 

That is correct, especially the beefheart mixes that they use.

I agree with you whole-heartedly. It sounds a lot like snake oil to me, but then i have absolutely zero experience dealing with discus. Or any other fish besides the happy, simple community fish.

The logic that most of the enthusiasts use is that, by having such large and frequent water changes, the amount of filtration required is much less. Most of them simply use 1 or 2 sponge filters in quite heavily stocked tanks, and change 50% of the water every day or second day.

The issue of the bioload/biomass/biofilm/whatever you wanna call it is a difficult one for me to get my head around. One of the first things i learnt about the fish keeping hobby was that beneficial bacteria hang around on the surfaces of objects in the system, being decor/substrate/filter media/sides of tank etc. Combine the surface scrubbing with undersized filtration and the water changes, and a lot of that BB gets removed, admittedly along with the bioload.

In my mind, from a totally theoretical stand point, having a large filter, some kind of nutrient export, a UV steriliser and being thorough with a surface cleanup should be plenty. The biofilm should be handled by cleaning biological media in old tank water and replacing mechanical media regularly.

I'm going to see if i can dig up any kind of literature around what the toxins that biomass releases are, otherwise it's just hearsay and anecdote.

 

Water changes for me are mainly to reduce waste in the water and to reduce hormones that stunt growth. Example of this is my pleco tank. There's about 30 bristlenose plecos in a 30L. Normally there's just my breeding pair in there and water changes went from one every 6 days to once every 2 day because of the increased bio load and the amount of food needed.

 

I will admit, i'm pretty skeptical about the whole GIH thing. I can understand the theory behind it, but finding any thorough scientific studies is kinda tough. If you know of any, i'll happily give them a read.

 

Interesting enough for a dirted tank it is recommended that water changes happen infrequently. I guess here the aquariast will test nitrates more often to ensure their level is adequate.

 

Just normally see a better growth in fish with more water changes and good food. I haven't seen a scientific study on it but then again I haven't really looked.

 

That is indeed interesting...would this be to aid with mineralisation?

 

Discus don't like bacteria, so cutting down waste in the water and wiping off bacterial film on the tank does help apparently.