I agree with your points above. Perhaps plants don't have a "stop" signal as much as they have a "don't start" signal. My conclusion that healthy plants tell algae to not grow (is it called alleleopathic compounds?) is due to observing how healthy plants mostly do not grow algae, but one sick plant or sick leaf in an otherwise healthy tank will grow algae, or seeing algae growing on rocks and decorations in well-lit areas but not on the plants in the same area. I have to ask why algae won't grow on those plants, or why it suddenly decides to grow on another plant.

No one has ever found an "allelopathic compound" secreted by an aquarium plan. People have tried, but with no success. Tropica scientists concluded that there is nothing there to find.

An actively growing leaf will be depleting the nutrients at the surface of the leaf. An unhealthy leaf won't be doing that, and if it is dying, it may be releasing a tiny bit of ammonia. That may be one factor.

Do you think that's the only reason why algae won't grow on healthy plant leaves? I would think it would be a perfect spot - lots of light and a host to sap nutrients from. If the plant can be getting enough nutrients from the water circulation to live, certainly algae living on the surface of a plant leaf could be even if you take into consideration the plant's intake of nutrients. For instance there are plants growing very near the outflow of my hob. The plants are 100% algae free, but the filter itself has algae on it. The water is rushing so fast that I'm sure a tiny decrease in the amount of nutrients near any given leaf would not be enough to convince algae not to grow there. There must be another reason?

The other thing is that you can have substrate in nearly the same location as a dying leaf and it can be growing NO algae, but the dying leaf has algae all over it. There is waste breaking down in the substrate, probably giving off a whole lot more ammonia than that one dying leaf, why doesn't it grow on the substrate AND the leaf? Why pick the leaf?

im interested to know, so how is this tank faring at the moment? i also have a non-CO2 shrimp-only tank.. i am researching all the info i can get to make my tank healthy and problem-free.. TIA

Thank you for your interest. Sorry I didn't get back to you earlier, was just busy a work. I started doing weekly 50% water changes and dosing excell along with EI dosing for excell method. I try removing algae almost every week, but it still grows on all older leaves, only new leaves are algae free. I think I only don't have algae on my flame moss. Plants do grow, but not very fast.Brown algae is mostly gone, but I think I have BBA and some green spot algae on plants. My light is not very high, it is 28W on a 20 Gal tank, so it's only 1.4w/gal

I have included pictures of my tank, so you can see how everything looks.

The leaves that have algae are probably getting algae due to not being healthy, that is, algae is a symptom, not a cause. Your low light levels may not be enough to reach the lower/older leaves and keep them healthy, hence they start dying off and algae opportunistically starts growing on the already dying leaves. If the issue is mainly algae growing on the plants, and not the substrate or glass so much, plant health is the issue.

Thank you Carissa. I noticed that higher plants, that are near the lights grow much faster and better than plants on the bottom of the tank. So I also had a suspicion that light wattage might be too low. It's just Tom Barr advised me earlier not to get stronger light, because higher light will cause algae growth. That's why I bought 28w t-5 lights (1x6700K bulb and 1x1000K bulb) . I am not trying to criticize, I just want to figure out the problem.

Algae is mostly on plants, didn't get to substrate yet, and glass gets a little bit of brown algae, but it's enough to clean it every few weeks.

I am dosing: Seachem Equilibrium 1/8 tsp 1 x week
Nitrate 1/8 tsp 2 x week
Phosphate 1/16 tsp 2 x week
Flourish 2ml 2 x week
Fluorish iron 2ml 1 x week
Excell 4ml daily
water change 50% every week

1.4 watts per gallon of T5 lights is equal to a lot more wattage of PC bulbs. I think you can assume you have the equivalent to 2 watts per gallon or a bit more, if you had PC bulbs. If anything you may have a bit too much light for an Excel only tank, in my opinion. I don't think low light is likely to be the problem.

You are dosing twice the recommended dosage of Excel, which should help keep the algae under control, but I know Tom always recommends following Seachem's recommendations for dosing Excel.

I don't really think this is a problem, but the 10000K bulb may be providing too large a percentage of its light in areas of the spectrum that the plants don't use, but algae can use. You really can't go by just the color temperature the manufacturer assigns to the bulb, so you would have to study the graph of output versus wave length to even guess whether this is a problem. That isn't something I am capable of doing.

This is the light fixture I have: 24" Aqualight T-5 - Double Linear Strip - 58020

It doesn't have a very good reflector, I think. It's just white plastic, and narrow, just fits over the light bulbs. Plant parts closer to the light are doing better than the ones closer to the bottom.


For now I'll try scaling back on Excel first to 2ml per day and see if that helps. And maybe I should replace 1000K bulb with 6700K.

Given that you don't have much of a reflector at all, and from the pic it seems like the tubes are a pretty tight fit, it could be that you are losing a decent bit of light to restrike and that inspite of the higher efficiency of T5 tubes you could still not be getting enough light near the substrate. It is hard to say though. It could also just be what Hoppy mentioned regarding the 10000K bulb. Most people who do use such bulbs in their tanks already have enough lighting from other bulbs so that the extra 10000K doesn't make too much of a difference.

Maybe Tom or someone else might have some suggestions. I hope you manage to fix your algae problem.