# Algae just at high levels of tank?



## LancsRick (27 Jul 2012)

Where my plants have grown within about 4 inches of the surface, I'm now seeing hair algae develop on their leaves. The rest of the tank is fine.

Am I right in assuming that this is due to the PAR at that depth of water becoming such that algae is thriving  as the leaves at that level cannot react fast enough? If so, I'm confused as to why it's so localised, since I'd expect the plant to react more as a whole instead of differently at levels?

Thanks guys!


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## ceg4048 (28 Jul 2012)

LancsRick said:
			
		

> Where my plants have grown within about 4 inches of the surface, I'm now seeing hair algae develop on their leaves. The rest of the tank is fine.
> 
> Am I right in assuming that this is due to the PAR at that depth of water becoming such that algae is thriving  as the leaves at that level cannot react fast enough?


Yes, I partially concur with this analysis. Photon flux varies according to the inverse square rule so that, for example, if a bottom leaf is twice as far away from the bulb than a top leaf, then that bottom leaf is exposed to 4 times less PAR than the top leaf. It is therefore much easier for the bottom leaf to deal with  less light than for the top leaf, which will need to process a proportionally higher amount of CO2 in order to avoid being damaged by that 4X higher level of radiation. So it is not so much that the top leaves cannot react fast enough, but that you do not have enough CO2 at the top of the plant to satisfy the amount that is demanded by those leaves based on the radiation flux.



			
				LancsRick said:
			
		

> If so, I'm confused as to why it's so localised, since I'd expect the plant to react more as a whole instead of differently at levels?


If you suffer an injury on your left hand, do you feel it on your right hand? Light does two things to plants; it provides energy for food production and at the same time causes radiation damage to the tissues. If there is enough CO2 and nutrition available then the plant can produce enough food to repair itself and add higher levels of protection to overcome the damage caused by the radiation. If there is not enough nutrition the rate of damage exceeds the rate of food production. The lower leaves must produce enough food to keep themselves healthy as well as to produce food and oxygen for transport to the roots down below. They cannot spare enough resources to send to the leaves above. Those leaves must fend for themselves. If not, then they are sacrificed because the overall health of the plant is more important. If you see the algae on all levels of the plant then that means there is poor CO2 at all levels, not just at the top.

This is why there is so much failure with planted tanks, because people automatically assume that light is the only important thing and that it makes plants grow healthy. A plant does not grow because of light. It grows and is healthy because of food. The light is an oven or a stove top that powers the reactions that make the food, but at the same time it is dangerous and if it is not fed with the other important compounds necessary to complete the process of food production it will be out of control and will annihilate the plant. This is why few plants can grow in a desert, because there is too much light and not enough water. For aquatic plants which have an abundance of water, there is too much light and not enough CO2.

Cheers,


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## LancsRick (28 Jul 2012)

Thanks Clive, logical and reasoned replies as always! I'll probably just trim the tops back and deal with it that way.


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## ceg4048 (29 Jul 2012)

Yes, that solution will work probably in the short to medium term. But we should consider it a warning sign for the long term. At some point, given the same level of CO2, flow/distribution and lighting the mass of the plants will increase, both above and below the sediment such that you might start to see the CO2 related stress even at deeper levels. A more permanent solution would be to reduce the lighting.

Cheers,


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## LancsRick (29 Jul 2012)

Knocked an hour off my photoperiod . Will that suffice or is it purely the PAR I'll need to worry about?


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## ceg4048 (29 Jul 2012)

Gosh, there is no way to tell other than to observe the tank, especially since I don't really know any details of the tank or what your prime objectives and limitations are. Generally speaking, photoperiod is only relevant within the context of the PAR levels, so one hour less may help or it may not. It's not clear what lighting is there or even if this is a Co2 enriched tank, or even what kind of plant we are talking about, so I can only make broad and general statements. In any case this is precisely one of those "reading the tank" issues that folks need to be aware of and to understand at a fundamental level because they are often harbingers of doom. There are several possible paths in which it can develop (good, bad or middling) because of all the variables, and there are therefore several paths to a solution. Severity and degree of difficulty on the chosen path to resolution is much more difficult to judge unfortunately.

A vague response, I know....sorry...  

Cheers,


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## LancsRick (29 Jul 2012)

Sorry Clive, I realise you get a lot of questions without really having a fair chance to answer!

It's a non-CO2 tank with two 18W T8s with reflectors, and 2 Eheim 2217s giving 2000lph of flow. I'll keep an eye and try playing around with the spraybar position to give stronger flow in that area.


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## ceg4048 (30 Jul 2012)

Hi mate,
            OK, it's non-CO2 which means your options are more limited. Is it possible to temporarily disable one bulb or to remove the reflectors or to add surface cover plants? This is a popular trick for the low techers in order to reduce the incident PAR. After a while you can increase the intensity. Depending on the plant it may take some time for them to adapt to the low CO2. Trimming will help, so I can see why you opted for this. The new growth should be better adapted.

Some plants don't fare so well and you are forced to at least supplement with Excel or equivalent, but others like crypts, ferns, mosses, vallis and some hardy stems adapt more easily.

Cheers,


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