Oxygen

[jeff_hopkinson]

Hi, i have not posted for a while but i thought i would try again. A planted tank, plants give off oxygen when the tank is lit, at night we have to turn up the air pumps to provide oxygen. what happens during the day when lights out for rest period are we suposed to turn up the air for that period then turn it of again when lights are back on. I know it sounds a silly question because i know a lot of you are not in during the day but it was just a thought. i am assuming that three hours is not long enough to cause any problems.

 

[CruX]

Oxygen naturally dissolves into the water, to aid this an air stone will aggitate the surface and increase the process.

 

[Jabba]

The air pumps only indirectly provide oxygen anyway by circulating the water for one and by agitating the surface of the water for another, very little O2 is disolved from the bubbles.

A lot depends on the tank construction and how much surface area the water has and how exposed to air it is, a lot of tank tops seem totally enclosed so I am not sure how many air changes the top of these tanks get. If you are concerned you could aim a spray bar across the surface from your filter discharge to agitate the surface, not sure how big your tank is but I wouldn't be overstressed about three hours with no airstone.

The one thing I'd be asking since you have plants is how you control the CO2 - an essential part of the photosynthesis process and therefore the oxygenation, if the CO2 isn't right you aren't getting the benefit from the plants that you might imagine, running an airstone knocks CO2 out of the water - bad for plants. Plus plants can turn a water from alkaline to acid (carbon stripping) as part of their life cycle so the CO2 levels is doubly important if you want a stable pH. Plus if the type of the light is incorrect then they don't photosynthesise well, so it's daylight tubes or even daylight itself from time to time, algae is not really a problem if you get the balances right and Algae photosynthesises too anyway so it isn't all bad.

Sorry sometimes I should answer the question alone but I think in this case you may be asking the wrong question. check this article out > The Role of PhotoSynthesis

 

[jeff_hopkinson]

Thanks, i try to follow what you are saying, my tank is a jewel180l and yes the top is closed but could be left open if needs be as i sometimes have to if it gets a bit warm. yes i have my spray bar rippling the top of the water but during the day i turn my air pump down so there is hardly any air being pumped into the tank as i know too much water movement is bad for the co2, by the way, i do not have the posh expensive co2 units only the fermenting ones but they still are doing the job. I fitted a j b l co2 test kit today and it reads a light blue colour which indicates that my p.h.is 7.2 and the co2 is o k. It was just a thought as to what happens, if anything, to the oxygen when the lights are out in the middle of the day.

 

[Jabba]

Generally there is enough stray light to keep somehting ticking over, if you only turn down the air and you agitate the surface I think you are good to go, it is possible to get obsessed with keeping the plants healthy and forget about the fish and make the fish suffer to avoid driving CO2 out of the tank.

I think the O2 in something like your tank will be 50 / 50, 50% plants, 50% water surface although I don;t know how densly planted it is. Remember though oxygen only gets in through the plants when the light is good but I think it is like a battery, the plants charge the water with oxygen (providing the photosynthesis is OK to begin with) so all you need to do is make sure the lights are correct for the plants and are on for a suitable period - I'm no sure I agree that 8 hours is a maximum - most days where tropical plants come from arelonger than that, if the tankis properly managed the plants will out compete any algae.

I doubt with the water movement and reduced air you have anything to worry about.

Just keep the airstones clear - those yeast based CO2 generators can clog them up quite badly.

 

[jeff_hopkinson]

Thanks, it was just a thought, my lights are on 9.0am till 1.30 then off till 4.30 on till 9.00pm so thats 9hrs litghing but i do have a 18w tube that comes on half an hour before the others come on goes off when the others go off then comes back on for the evening time but goes off at 9.30pm, if you can follow that. the other question is why turn the lights of in the middle of the day ( in the wild in the rivers were these plants originaly come from nobody turns the daylight off there they are used to at least 10hrs daylight ) or even 12hrs. so why do we turn our lights off.

 

[Jabba]

I think because some people are terrified of algae, algae is a plant like any other, it must compete for resources so in my opinion I think you will only get algae if the plants aren't healthy or you don't stay on top of the water changes or water chemistry - the plants should take up a lot of the available nitrate but they won't consume all (depending how many fish ar in the tank of course) so it is up to the fishkeeper to make sure he gets rid of the rest. (recommended minimum is 20ppm Nitrate for a planted tank)

I tend to run my lights from 10am to 8pm ish then I switch to the 'blue / grey' lighting to simulate moonlight until I go to bed, I have no algae problems at all.