Water Changes - Once a Month?

RaymondL · May 31, 2023

In my 9 month nano tank of 13.5 Gallons (Fluval Evo), I typically do water changes every week, but recently I went away for 2 weeks and left it as is and on the 3rd week I tested the water with the following parameters:

Ca: 420
Mg: 1385
Nitrates: 2.1
Phosphates: 0.03
dkH: 8.3

After 3 weeks of no water change, I thought that the nitrates/phosphates would be elevated, but clearly they weren't. I am dosing Ca, and Alkalinity via dosers as well to keep them numbers up.

Given the above results, I'm wondering whether I can stretch water change to 1x a month, or even longer once I determine how long I can go before I see a spike in Nitrates/Phosphates - is this a bad plan?

My concern of course is not replenishing the water results in depletion of trace elements, so unless I dose those specifically - then again, I would need to send a water sample after 3 weeks for and ICP test and see what is lacking, and dose accordingly.

Thoughts?

jda · May 31, 2023

If you are skimming, then longer periods between water changes are fine. If not, then you need to change water to remove harsh metals that bind to organics.

Water changes are not a good way to control phosphates since they bind to the sand and rock and only a small portion of them are in the water column.

Water changes can replace trace elements in an amount that you do not have to worry about. They will not build up like when using a supplement with many things in it.

You can buy 200 gallons of salt mix for less than a single ICP test. For a 13.5g tank, there is likely no cheaper or easier way to keep elements in check than just changing water.

srobertb · May 31, 2023

RaymondL said:
In my 9 month nano tank of 13.5 Gallons (Fluval Evo), I typically do water changes every week, but recently I went away for 2 weeks and left it as is and on the 3rd week I tested the water with the following parameters:

Ca: 420
Mg: 1385
Nitrates: 2.1
Phosphates: 0.03
dkH: 8.3

After 3 weeks of no water change, I thought that the nitrates/phosphates would be elevated, but clearly they weren't. I am dosing Ca, and Alkalinity via dosers as well to keep them numbers up.

Given the above results, I'm wondering whether I can stretch water change to 1x a month, or even longer once I determine how long I can go before I see a spike in Nitrates/Phosphates - is this a bad plan?

My concern of course is not replenishing the water results in depletion of trace elements, so unless I dose those specifically - then again, I would need to send a water sample after 3 weeks for and ICP test and see what is lacking, and dose accordingly.

Thoughts?

You don’t mention what’s in your tank.

it is 100% possible to run a tank with zero water changes. I know this because I am doing this very thing in a 10g AIO. Everyone has different definitions of success but I think the tank has been running for 5 years now.

Filtration has been provided by: Nothing. Just some gulf live rock. About a year ago in an effort to do “something” I started changing out a bag of chemipure every 3 months. I bought the IM manual filter sock roller and that’s been installed for a month or so. I turn the knob every week or so.

I have rockflower anemones and a CSB bubble tip in the tank. No fish. No corals. Feeding is a sprinkle of dried pellets once every week or two. Spot feeding anemones frozen or fresh food should be more frequent but it’s been a month or two.

I have no coraline algae. I dosed all-for-reef for about a month and saw a spot on the back wall. I have since neglected to refill the reservoir and the spot went away but the annoying emails persist so I should probably fix that today. (The error alert on my hydros, the All for reef benefited nothing).

My parameters are as follows:

Nitrates: No idea. Haven’t tested in years
Calcium: See above
Alk: No clue
Mag: Lol
PH: Id guess between 5-15 but I’ve never tested.

If I had soft corals, I’d probably run everything the same. Using a good quality food is a good way to add what may be taken up by the tanks inhabitants.

If I had hard corals (LPS or SPS) I would have concerns (depending on colony size) if my alkalinity and calcium didn’t consistently fall. I think in smaller tanks with more fragile inhabitants, weekly is the way to go.