Almost 3 weeks (19 days) without a water change.

[duanes]

I normally try to do around three 30% to 40% water changes per week , but I had to go to the states for 3 weeks, so although I had friend top the tank off for evaporation (to keep the pump submerged) , no water changes were done.
It is a 180 gal tank, home to some tetras (a Machaca 6" and a few Astyanax tetras 3"), 2 Gobiomorus dormitor gobies (one about 6 "), 2 Awaous banana Gobies (@ 5") and 2 Andinoacara coerleopunctatus cichlids (@ 4").

The Machaca above (Brycon beherae),, Astyanax below.

Gobiomorus dormitor above, Awaous banana below


Andinoacara coerleopunctatus below

The tank is filtered by a 125 gal very heavily planted sump (Valisneria, water lilies and mangrove tree saplings)
80 % of the sump dedicatcated to plants the other @ 20 % has some bio media, a square of Porrett foam and the pump.
The sump below

Todays test results below

The results above, as I interpret them
1st tube on the left, normal pH range reagent overwhelmed by tanks higher pH (way too dark blue to accurately read)
2nd tube, High range reagent pH = 8
3rd tube Ammonia 0
4 th tube nitrite 0
5th tube (far right) Nitrate almost undectable
Meaning my plant filter, is actually doing what it's supposed to do, eat nitrate as fast it is produced by the fish, and other metabolism, even after almost 19 days without a water change.
Mangrove saplings below

 

[Preacher]

That’s awesome!

 

[Ansorgii]

With that many plants I am not surprised. I keep 4 Oscars in a tank with a less green and it still manages to let the nitrate sink from the tabwater level.

I also try to change as little water as possible in general, unless I want to simulate the rain season, it just ads stress and my tabwater is worse than my tankwater anyways, so I'd rather invest in a good filtration. I do remove plants and excess mud from my filter tho.

 

[duanes]

The one obvious difference over 3 weeks, was the tetra population.
Before leaving for the states, there were around half dozen Tetras.

This population of Tetras has dropped significantly (not a surprise), to 2 or 3, and the Gobiomorus goby has grown significantly.

 

[OutbackJack]

my fiancee's tank got SO overran with water lettuce that we really didn't have to worry about water changes.

Water is crystal clear, all the parameters are perfect, and as long as the sand was vacuumed, it was never dirty lol

 

[esoxlucius]

Given your situation duanes , what with your heavily planted and low stocked tanks, not to mention being outside where rainwater can top up too, I'd be surprised if you ever registered nitrate, even if you never did any water changes, ever!

At the end of the day your tank is a miniature outside waterway, and benefits immensely from being so.

The water changes that you do, I'd say, are nothing to do with nitrate control, your plants deal with that. Your water changes just freshen things up and replenish lost nutrient, but even saying that, the regular rainwater your tanks get can do that.

Basically you shouldn't have the need to do any water changes, other than perhaps during the dry season when regular influxes of rainwater are not available.

 

[duanes]

Given your situation duanes , what with your heavily planted and low stocked tanks, not to mention being outside where rainwater can top up too, I'd be surprised if you ever registered nitrate, even if you never did any water changes, ever!

This may be an interesting experiment to try.
Now that its the dry season, to forgo water changes to just see how (or if) long it takes to start to register nitrate.
And at the same time, determine if other water parameters are effected by the different regime.
And or if fish show anynoticable effects.

 

[Lucifer0411]

Thanks heaps for sharing that. I'm trying to sort a solution for my 10 ft 330G tank full of cichlids & silver dollars etc. My only tank out of 7 which isn't heavily planted for obvious reasons. I have a 75G gathering dust so would love to do something like what you have done. The only thing is my tank isn't drilled and not going down that route. If I can figure out the sump without drilling I'll definitely give it a go.

The other tanks I'm down to about once a month changes and even then could extend it. The large tank however has to be done weekly due to nitrate buildup.

 

[scottts210]

Excellent results. That sump is awesome.