Can I turn the pump off?

[Corydoras_Catwoman]

I’ve got a completely DIY planted tank going for my bedroom. It’s only a 15l tall tank (I re-siliconed an old reptile enclosure and installed gaps for piping) so I’ve made a homemade filter from some parts I had lying around. It’s got a chamber with some ceramic filter media and an external sponge, and then a head that oxygenates at the surface. My question is, how damaging would it be to turn this off at night? (8-9hrs) It’s planted up with some nice ludwigia, micranthemum, etc, which all seem to do fine with the low flow as it is...my worry is obviously with the bacteria, although the media chambers have holes exposing them to the water all of the time anyway. It’s only for plants at the moment, although I’ll consider adding a pair of neocardinia davidii or such like later on. What are everyone’s thoughts?

 

[Abaddon]

The nitrifying bacteria need oxygenated water passing over them constantly or they'll start dying off. Exposure to water is not enough, they need water movement. Turning the filter off at night is pointless, might as well not have one at all. Besides, without surface agitation there will be less oxygen in the water, and that could be a problem for any animals you might want to add in the future - especially since oxygen levels drop naturally at night due to plant respiration, which could lead to hypoxia. Also, without proper water circulation, there is no even distribution of nutrients for the plants. Plus - a filter that's been turned off for many hours and then suddenly turned on again can start regurgitating all kinds of gunk back into the water, including potentially toxic hydrogen sulphide.
If I were you, I'd either go filterless & heavily planted with minimal fauna, or keep the filter turned on 24/7. Constantly switching it on and off is not a good idea.

 

[Corydoras_Catwoman]

The nitrifying bacteria need oxygenated water passing over them constantly or they'll start dying off. Exposure to water is not enough, they need water movement. Turning the filter off at night is pointless, might as well not have one at all. Besides, without surface agitation there will be less oxygen in the water, and that could be a problem for any animals you might want to add in the future - especially since oxygen levels drop naturally at night due to plant respiration, which could lead to hypoxia. Also, without proper water circulation, there is no even distribution of nutrients for the plants. Plus - a filter that's been turned off for many hours and then suddenly turned on again can start regurgitating all kinds of gunk back into the water, including potentially toxic hydrogen sulphide.
If I were you, I'd either go filterless & heavily planted with minimal fauna, or keep the filter turned on 24/7. Constantly switching it on and off is not a good idea.

Okay thank you for such a detailed response. I’ll leave the filter on 24/7 now

 

[NannaLou]

The nitrifying bacteria need oxygenated water passing over them constantly or they'll start dying off. Exposure to water is not enough, they need water movement. Turning the filter off at night is pointless, might as well not have one at all. Besides, without surface agitation there will be less oxygen in the water, and that could be a problem for any animals you might want to add in the future - especially since oxygen levels drop naturally at night due to plant respiration, which could lead to hypoxia. Also, without proper water circulation, there is no even distribution of nutrients for the plants. Plus - a filter that's been turned off for many hours and then suddenly turned on again can start regurgitating all kinds of gunk back into the water, including potentially toxic hydrogen sulphide.
If I were you, I'd either go filterless & heavily planted with minimal fauna, or keep the filter turned on 24/7. Constantly switching it on and off is not a good idea.

I’m not certain that this is 100% true. I’m in the process of building a low-tech/Walstad style tank where the plants become the filter.

My plants have only been in for 1 week, but I don’t have a filter or artificial lights. I do have a heater as I plan to have fish at some point that will need heated water.

 

[Abaddon]

I’m not certain that this is 100% true. I’m in the process of building a low-tech/Walstad style tank where the plants become the filter.

My plants have only been in for 1 week, but I don’t have a filter or artificial lights. I do have a heater as I plan to have fish at some point that will need heated water.

That's a slightly different story. The OP didn't mention anything about wanting to use the Walstad method (which, btw, does sometimes include a pump or filter for water circulation/backup filtration). A heavily planted & understocked tank with proper substrate etc. can run without a filter, but unless you really know what you're doing it can still be a bit of a hit and miss.
Regardless, there's no point turning the filter on and off all the time. You either have one and keep it on 24/7, or you don't have one at all - but then you need to do your research and pay extra attention when setting up the tank.