Would the amount of water changed per week differ after adding a sump?

[ilaizm]

If you have a 95G tank with adult discus set on a regular water change regime which works well. I will not go into how many times and volumes here as I know everyone would have a different opinion on this. Say you have a regime which works, and you now add a 30G sump. Would the same amount of water changed per week be enough or would you have to increase the amount of water changed to reflect the extra 30G of water?

[Lenin]

It all depends on how much water you're changing and how often, without that there's really no way to answer the question

[ilaizm]

I change 50% once a week or 25% twice a week.

But let me rephrase my question... If you had a 95G setup with a canister filter and calculated how much water you need to change. Once you have a 30G sump, when calculating do you consider your tank as holding 125G of water?

[Lenin]

Yes, you would calculate the water in the sump, personally I would do the 50 instead of the 25x2, I would suggest 70-80 per week

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[ericatdallas]

Assuming you have the same bioload and you want to maintain the same ppm contaminants then you have to increase the WC proportionally to your increase in water volume.

I do think with a larger volume could lower your WC because the dilution is greater but your contaminants would flatline at a slightly higher level. So it depends on the metric you're using and what you want to control.

I also would recommend larger WC to two small WC of equivalent volumes as Lenin said.

[Trier20]

When I added a 30g sump to my 90 I assumed it to be a 120g tank and did 60g WC's daily.


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[YSS]

Same amount. Why would you have to do bigger water changes? It's the amount of water you change that matters. Not percentage of total water volume.

[Wjmulder]

It's the amount of water you change that matters. Not percentage of total water volume.

You need to explain that one, I'm not following

[tannin]

If you are concerned about dilution of the undesirable stuff in the water, then it is indeed percentage that matters, so you need to change more water because of the greater volume. However, offsetting that will be what you use the sump for. If the sump contains methods of removing undesirables, like skimmers, algae scrubbers, etc then the amount of water change required will be less. The net effect may be no change at all, or even a reduction :).

btw: 25% twice a week is not the same as 50% once a week.