Algae all over the place

[Yéri]

Hi Guys,

Our 4 months old greenhouse is have its first issue so far: algae!

We keep our seedlings wrapped in sphagnum moss in trays and most of them have a brown layer of algae on top.

Rather than spray Physan 20 (which I read might be harmful to seedlings), I bought Agralan Citrox in order to contain the damage. Seems to have stalled it for a bit, but I'd like to avoid any future outbreaks.

As the algae seem to be developing in our water reservoir inside the greenhouse, which sits on a heated floor, I'd like to neutralize the algae between that reservoir and the watering hose.

The water is smelly as well when it comes our of the hose, so plenty of bacteria as well in there I suppose.

After consulting a few websites, my best guess would be to install the following: Mauk 601 Kombifilter UV-C Netz-/Aktivkohlefilter, 7 W: Amazon.de: Garten

This would (or should) eliminate any algae or bacteria going through the filter. Unfortunately, I don't see anyone having tried this with watering orchids. I have a PP filter like this installed for the automatic misting system in the greenhouse, and that water seems to be devoid of any odours, so that seems to work just fine.

Might there be a downside to using this when watering our orchids?

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[Ray]

Any time you have water + nutrition + light, you're going to have algae growth.

On the greenhouse hardware, it can be an indicator of over-fertilization. In the water tank, the best thing you can do is block the light from getting to it. The smell of the water suggests the algae is dying.

Prevention is better than correction. The UV rally isn't going to do very much, and those filters are going to clog pretty rapidly.

I never had an issue with seedlings and a mild dose (1:200) of Physan, but I switched to Biosafe Disease Control, as it displays no phytotoxicity whatsoever.

[Yéri]

Originally Posted by Ray

Any time you have water + nutrition + light, you're going to have algae growth.

On the greenhouse hardware, it can be an indicator of over-fertilization. In the water tank, the best thing you can do is block the light from getting to it. The smell of the water suggests the algae is dying.

Prevention is better than correction. The UV rally isn't going to do very much, and those filters are going to clog pretty rapidly.

I never had an issue with seedlings and a mild dose (1:200) of Physan, but I switched to Biosafe Disease Control, as it displays no phytotoxicity whatsoever.

Hi Ray,

Thank you for that clear explanation.

Here's a couple of pictures to give you an idea of my situation, as the points you've made don't always seem to apply to my greenhouse setup.

First of all, here's my water reservoir inside the greenhouse (front and top view). There's barely any light coming in, is that still enough to cause algae to grow inside?



Here are the trays and some mounts, some of them were pretty dark brown, but the plants don't seem to suffer from it (yet)



And last is the water reservoir outside, from which the water gets pumped into the reservoir inside the greenhouse. It's still open right now (the concrete cover broke), but again I didn't detect any smell or extensive algae growth inside.


So I don't think light getting inside the tank is an issue here. Overfertilization would surprise me, as I always use lower levels than recommended, and didn't see any other signs of overfertilizing my plants.

I went to the greenhouse tonight to check the water, and no smell whatsoever to be detected, so might it be the daily heat that triggers the smell/decomposition?