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Discussion Starter #1
Happy new year everyone!
I'd really appreciate your thoughts on an algae problem that I think might be the result of something I'm doing wrong, though what that is I don't know! There's brown algae growing all over my plants. They grew really well when I first set up the tank (http://www.aquaticplantcentral.com/forumapc/el-natural/56861-conversion-4-foot-tank.html) and we just had a bit of green algae for a while. Now that the green algae has subsided, brown algae has taken over and is growing on the leaves of all the plants (except the vallisneria and hygrophila - weird) and smothering them. They're not growing at all and some of the swords have actually melted under it. It's also all over the glass and I have to wipe it off every few days.

It's summer now and during the day the temperature of the water gets to 28 C, sometimes up to 30 C (86 F). Is the heat stalling the plants' growth and allowing the algae to take over? Or is something else going on?

The lights are on for 12 hours a day, and the tank gets about an hour of filtered sunlight through a nearby stained-glass door.

Something else that's strange - the pH is unstable. Goes up to 8.5 during the day and heads back down as the tank cools off in the evening. ????
 

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There are a few problems I see with the tank. One the temperature is quite high, most plants won’t be able to handle this kind of heat. Though amazon swords should be ok in it.

The pH swing isn't that strange. In the day plants use CO2. Since CO2 makes a weak acid when mixed with water called cabonic acid, when the plants use all the CO2 they remove acid from the water and the pH goes up.

At night when the plants have no light they break down sugars and release CO2 into the water causing the pH to drop.

If you have power compact lights or another intense light then I agree with queijoman you should reduce your light time especially since you are getting direct sunlight from the window. Try cutting the lights down even more to 7-8 hours. Your plants won't be able to take advantage of all that light unless you have pressurized CO2 and a fertilization schedule.

Speaking of fertilizers, what are you adding for nitrogen? Amazon swords are very nutrient hungry plants, it may be that they have simply run out of food. If the new growth is pale, or white compared with the old growth then you have a nitrogen deficiency, or possibly an iron deficiency.

As for the brown algae, this tends to happen in new tanks that have just been set up, or in tanks where the light levels are too low (if you have intense light then this is not the reason you have it), or if the tank is dirty. Brown algae is not a real algae, it does not need light to live, it is a flagellated single cell that eats decaying matter in the tank. When you wipe it off the glass it just swims back and sticks to the surface again.
 

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just want to talk about the benefits of ramshorns again. :D
They graze on glass and leaves, eating algae films. They are not very agressive plant eaters and relativly easy to control.
'Tropical tank tribes' are not overly temperature sensitive too.
Regards
 

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Ah... didn't see this was posted in the natural forum. So you probably don't need to add nitrates if you have soil.

Please post more info about your tank so we can help diagnose what is wrong
 

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Discussion Starter #6
Thanks for all the replies!

The plants are growing in soil capped with gravel, in trays. They grew so well during the first month or so, then stalled and the algae got on top of them.

I'm used to getting algae problems in my "high-tech" tanks when setting up a new one, and it always subsides after a few months of its own accord once the plants get going, but this tank seems to be working in reverse - the plants took off right at the start, then started to die back as the algae took over.

There are pond snails in the tank but they don't seem to have any real impact on the algae.

I had a close look this morning and the algal mats that are growing on top of the plants seem to be a mixture of different types of algae - mainly brown, like the stuff that gets on the glass (diatoms?), but also furry red and black algae, and a little bit of green spongey stuff. On the surface of the water is green stringy algae but the fish seem to like eating that so it isn't a problem.

The lighting is 2 banks of 2 compact fluorescent tubes (approx. 2W per gallon). They generate a lot of heat, so I have only been keeping one bank of them on for most of the day (1W per gallon). There's a siesta of an hour mid-afternoon.

Water circulation is provided by a submerged powerhead.

The tank is quite deep (80cm), so there's a lot of glass for algae to get a toe-hold.

I'll cut down the light and hope that makes a difference. Thanks :D
 

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On another note, is your soil anaerobic? Are there bubbles of bad smelling gas coming up from the substrate?

It might be that the soil has gone bad is fouling the water causing the plants to decrease in growth.

Also make sure you do partial water changes every so often, I found that even in my soil tanks this does help replenish some nutrients that may not be in the soil in very high amounts.
 
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