planted tanks and o2 levels

[aspen]

this is a question that has been bugging me for a while, and i believe that i have finally found an answer, in this article:

http://edis.ifas.ufl.edu/FA002

o2 levels in ponds are described. they can get seriously low, during the night, up to dawn, before the sun comes up. this is related to home aquaria, as to how many plants and fish that you have in your tank, and how much water volume that you have, that can dissolve and hold that dissolved o2.

for example, if you have a light fish load with small fish (low o2 levels consumed from the water column at night), with a tank that is planted only say 1/2 of the way up the water column, the amount of o2 consumed will not be that much before the lights come on, when the o2 levels are replenished. but if you have a lot of plants, and many large fish, then the o2 users quickly use the o2 to dangerous levels before the lights come back at dawn.

the answer seems, that if you cannot find a better way to replenish o2 at night, then you must keep the water to fish/plants ratio high, thereby having plenty of o2 dissolved to last the night.

please note, that algae will die off first, before the larger plants will. this may be why the algae all of a sudden disappears in a planted tank, after some time. this is observed by many planted tank owners. maybe the plants are growing fast enough, that they are able to starve the water column enough, that the algae cannot survive through the night. but i wonder what this is doing to the fish? obviously, this last point is highly speculative.

rick

 

[jowens]

One way to address oxygen depletion at night is to set a airstone on a timer to go on for a couple of hours in your tank late at night. If you're running CO2 into your tank, you'll typically starting getting high CO2/low O2 in the early morning hours, when your tank lights have been off for a lont time. But even if you're not running CO2, you can still have O2 depletion problems - so this works in either case.

Simply hook up your airstone to a timer, so that it turns on for 2-4 hours at night, during the time when the lights have been off the longest. The resulting surface disturbance will allow O2 to enter the water, while releasing excess CO2 that has built up over the course of the night.

If you're injecting CO2, I wouldn't recommend leaving the airstone on for too long. The point here is to let some O2 in - not let all the CO2 escape from the tank (resulting in pH swings). By just running the airstone for a couple of hours, you compensate for the nightime dip in O2 without compromising your water's chemistry by overdoing it.

I would not recommend turning your CO2 on and off to compensate for O2 depletion. The resulting pH swings would most likely do far more harm then good. Using a small airstone, you can get a similar effect while causing much smaller pH fluxuations.

 

[jowens]

please note, that algae will die off first, before the larger plants will. this may be why the algae all of a sudden disappears in a planted tank, after some time. this is observed by many planted tank owners. maybe the plants are growing fast enough, that they are able to starve the water column enough, that the algae cannot survive through the night. but i wonder what this is doing to the fish? obviously, this last point is highly speculative.

Rick - it's often thought that the reason algae dies off suddenly while plants survive has to do with phosphate levels in the aquarium. It seems that plants can live without phosphorus and most algae cannot. So in a planted tank that's been running for a few months, the phosphorus eventually runs out - killing the algae while the plants continue to live on just nitrogen (this is why you shouldn't ever add phosporus to the water). Building upon this theory is the idea that algae - since it consists of single celled organisms - lacks the ability to "store" food. Each algae "cell" needs a constant stream of neutrients, or it dies. Plants, being more complex organisms, can store neutrients in their leaves, roots, and stems - making them better equipped to deal with neutrient starved conditions.

One reason you should never use "pH down" is because it contains phosphates.

I'm not sure where oxygen depletion fits into the plant/algae picture...but I suspect that many fish would die of oxygen depletion before algae would. One of the big problems with algae is that it depletes O2 levels in water, causing fish to asphyxiate. So it seems like it's the fish who expire first when it comes to low O2 levels, not algae.

 

[farm41]

It's not the phophorus that causes algea, I add KH2PO4 to my tanks weekly and keep my P levels .5-1 ppm. My tanks have never looked better since using P, but you have to running enough light and co2.

 

[aspen]

j, the sears conlin report (pmdd dosage etc) is the basis for a lot of the info about starving P to keep algae in check. it has been used as a bible for many planted tank owners for some years since it's internet debut. but i have to question that, when successful planted tank keepers like farm report maintaining levels of phosphates in their tank, and being also algae free. the theory sounds good, but in practice, it seems smart to starve the water column (ime) for long enough for the tank to reach this algae free state, then things get real easy all of a sudden, and algae couldn't grow if it wanted to. this is the big reason why people don't start a tank with fish, so they can control the nutrients that would otherwise be going into the tank, as food.

fyi, i kept a tank for some months that was P deficient in the water column, adding substrate P only, and never getting a P test kit reading. yet, the algae persisted until it just 'went away'. i wish i knew what the 'golden bullet' is. but i don't, but i'm always open for dialogue, on this 'the most common planted tank complaint'.

have a nice day, rick

 

[jowens]

Yeah, the "golden bullet" is certainly ellusive. I'm currently having problems with black brush algae in my big planted tank. I just plug along, cut away the leaves it infests severely, and cross my finger that the magic moment arrives one of these days and it simply dries up.

It actually looks really cool on the wood and filter intake, flowing nicely in the water, but it's not too attractive growing on plants. Still, it's better than green slime algae, IMO, since it seems to take BBA quite a while to choke out a leaf as it only grows heaviely around the perimeter of the leaf. It seems kind of useless to try to manually remove it.

Oh well. Such is the life of the planted tank owner. I will persist and battle on...

 

[jowens]

Found this interesting article on Algae. It's good because it links to a lot of other, more detailed explanations of various theories.

http://www.skepticalaquarist.com/algae.html