Do I even need to do a water change?

David R

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It's been a week since my last water change, I usually change 10-15% on Wednesday, and this time I thought I'd test the water before hand...

test.jpg
tds.jpg

Ammonia: 0, Nitrate: 5ppm, TDS: 46ppm.

Tank in question is the one in my sig; 2000 litres, big sump with 20L of pond matrix, poret foam and pothos. Stocked with a 12 medium sized plecs and a bunch other small-medium sized fish fed 2-3 times daily on NLS food.

I'm going to do a water change anyway as I need to vacuum up some sawdust, but it does make me wonder if I'm gaining anything by changing any more water than is needed to do the vacuum, or am I just jacking up my power bill. I'm perfectly happy only having to perform small water changes, mainly because we rely on rain water to supply our house and only have one 25kL storage tank, and if we have a dry summer it can get pretty low, but also because of the time and electricity involved (especially over winter). It also means I don't have to stress about who looks after the tank when I go away on holiday, I've left it two weeks with no wc and the parameters were still very good. Magic stuff that pothos...

I'm sure someone out there will insist they'd still do 50% weekly on this tank regardless of the test results, but if it were up to you would you even bother doing a wc?

test.jpg

tds.jpg
 

MilitantPotato

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My only real fear about not doing regular water changes with tests coming out like that would be a PH crash, and the build up of the nasties that aren't tested for. I'd love your TDS in my tank. Mind shipping what ya siphon out to me so I can cut my tap water?
 

Ponera

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Just going to comment that one big source of oxygenation for some tanks can be water changes. If you have a bubbler or adequate oxygenation from obvious places then ignore this. That's my though on it.

I suspect not many people will engage full force into this because of the obvious: you are basically asking for a reason not to do water changes (universally good) and have evidence for a small bracket of time that you may not need to do them in a small bracket of time.

It's entirely probable that it is possible to make a closed system that is fully sustainable though trying it would be rather tough and risky, given all the living participants come from open systems.

Can't really say more than that!!! Good luck sir.
 

Woefulrelic

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Metals, among other things, will build up as you top off since it doesn't evaporate. That said you might be able to get away with biweekly or less frequent water changes. Someone with more knowledge will probably pitch in.


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David R

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Not sure where the metals are coming from, the tap water I use for water changes has a TDS of 006-008ppm! May take a while for them to build up to dangerous levels, especially given that there is virtually no evaporation from the tank.

I suspect not many people will engage full force into this because of the obvious: you are basically asking for a reason not to do water changes (universally good) and have evidence for a small bracket of time that you may not need to do them in a small bracket of time.
Not really, as I said I still changed 200L (10%) of water today so I could siphon out physical waste and for the "unknowns", I'm simply interested in stimulating some discussion on how much water needs to be changed in an aquarium, for those who don't buy into the "50% twice weekly, just because" sort of mantra. You raise a good point about oxygen too, I hadn't considered that but I think you're right.

Militantpotato, pH crashes are a real possibility with my soft water and huge pile of wood, but the substrate [partly beach sand] has a good quantity of crushed shell and there is a container of coral bits in the sump too. I take it the rain water in your area is no good to collect?
 

duanes

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2-5ppm nitrate is what I shoot for, with my water changes, so seems like you may have found a great balance of plant to fish ratio.
And with the low TDS in your makeup water, any metal/salt buildup should be minimal.
As long as growth is normal, hormones and pheromones aren't a problem, which are also removed with water changes.
 

David R

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Do you think that for the purpose of removing more "old" water, I'd be better off doing 20-25% fortnightly rather than 10-15% weekly?

I'm still unsure about hormones etc, but I've recently added a bunch of young fish so we'll see how they grow. My L190 royals aren't growing particularly fast, but that is par for the course.
 

duanes

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I find it easier to small more frequent water changes, but I just turn a valve and water is sent to my garden while I feed the fish or do something else, so I suppose its a personal preference.
And if your tanks pH doesn't change much in 2 weeks, why not.
I'm doing an experiment where I have a group of Tilapia, and some Nimbochromis growing up together in the same tank. But I've taken a single individual of each species and put them in a separate tank (with some other species) to see if the group grows slower or faster than the individuals.
Both tanks have a similar stocking level. Whether it is individual species hormones, or something else that makes a difference I can't be sure. But as of now, both the single Tilapia and Nimbochromis are about 25% larger than the group growing together.
I try to feed the same amount, and both tanks get the same frequency and volume of water changes.
These pics are not sequential though.

group above, individual below


 

David R

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Interesting experiment, and interesting that both individuals are larger than the groups. I guess there is a chance you may have picked out two faster growing individuals, but it would be pretty slim.

Water changes are easy enough on this tank as I have a drain in the sump, so like you it is just a matter of opening the valve and putting new water into the tank. The dilemma is that in summer I have to try to conserve water so don't really want to do big changes 'just in case', and in winter when we have ample water I'm limited to pre-heating 220L at a time, and big water changes straight from the tap will drop the temp more than I'd like. TBH I hardly ever check the pH now the tank has been running over a year, it seems to be reasonably constant throughout the week. Maybe I should try leaving it for two weeks and monitor it to see what happens. I usually do a "big" water change every fortnight (siphon settling chamber, rinse poret foam, more thorough siphon in the tank) alternating with a quick change of ~200L to remove the worst of the physical waste from the tank.
 
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