My greenhouse walls (rigid polycarb) need to be cleaned of algae in the worst possible way. I have a pressure washer I can use for the outside walls, and some of the interior walls. But in places where plants are actually present against the walls or growing on totems up the walls, I can't use it and will have to clean by hand. Using bleach is out of the question. I used to use Physan 20 back in the day, and can still get that, but wondered if anyone had better luck using something else? I am hoping for something with residual effect so that it won;t come back as quickly and maybe I can keep ahead of it.

Gina all I have ever used is Physan. It is ok but not great. Wish I had something better too.

I ordered a gallon, its a lot cheaper than buying by the pint and I know I will need it again. This is going to be a big job. 1740 sq ft of 12 ft high at the top edge wall space. I am thinking of using a swimming pool brush to clean the roof.

I use a microfiber sleeve on a long window cleaning pole that does telescope. Ettore brand. It actually works very good. I can clean the outside with no problem and the inside in the summer when most of the plants are outside. And I can also clean my windows. I buy Physan by the gallon too and actually need some more. I still wish there was something better. Algae is a big problem.
Michael

Yes it is. We also have very hard water so that is an issue on my walls too. My greenhouse has a 20 ft ceiling and there are some trees around it, so every year pollen falls on the roof (oak, cedar, pine) as well. I am going to scrub it this year and get the crud off so I get better light.

Yes I do this every year. Of course mine is not as tall as yours and easier to do. Same problem with the hard water on the interior walls.

I don't have any trees or shrubs near mine, but I do have the very hard water. I just try to keep all water off the inside glazing. I'm finally seeing some black mold in spots on the inside. It's been 3 years now since construction. I'll have to clean it off soon. I'll find some Physan.

I never heard of Physan until I read this thread. I was just about to use a bleach solution on the backs of my two solar collectors that are starting to show some black mold (I think)...probably because the rear of these collectors never get any sun. Went to their website and read all about it. Just bought a 16oz bottle online. I'm going to clean the whole greenhouse with it.

Jim its been around probably since before I was born (just kidding). A lot of orchid growers used to use it which is how I came onto it. You can sterilize tools, put directly on plants, and use on benches, pots and walls. I don;t use bleach on the inside of the GH because of the plants, but also because I read a long time ago that it can react with the polycarb and cause a gas to form that is toxic

I have hard water here and find adding vinegar to the water helps prevent water spots. I don't think that would hurt plants but might work for a rinse. Or do you leave the Physan residue on surface?

Kristin, you leave it on. It has residual effects that last a while especially on hard surfaces.

Made my first application of Physan today. Since my build up is heavy in some places (like this) I am going to leave it on overnight, pressure wash it off tomorrow, then reapply my stay-on residual coat. I could hear the bacteria, mold spores, viruses and algae screaming 'NOOOOOOOOOO.....'....

Yes Physan has been around longer than me too. I spray it on the walls, ceiling and plants. When I used to grow a lot of orchids I also soaked my tools in a cold tray filled with Physan. There used to be a generic brand used in swimming pools, I think, but I never used it. It was cheaper than the brand name.
Diluted bleach has been said to be harmful to the polycarbonate so I never used it on my greenhouses. I would not advise doing that.
Michael

Yes there was a very contentious thread once on another gardening forum I belonged to talking about bleach and polycarb. Also some people say that the strength of the Physan you get now is not the same as it was back in the day...but I think it is still just as effective as ever. I have used it on orchids too...and I have used it at a dilution of 1-2 tsp/gallon to kill the various molds and fungi and algae that form on the leaves of some plants because I had (before I turned it off and started hand watering) an overhead sprinkler system. You have to wash it off but it works well. I am going to disinfect some large growing Anthuriums and Palms tomorrow.

I have used bleach not the concentrate but regular strength for over 20 years inside and out side my greenhouse with power washer. It's a great way to disinfect the area less diseases. Better air circulation may be necessary to help in areas with a greater build up or even add a wall vent .

I read a article about bleach and plant safety, it's the sodium in the bleach that poses the most risk to plants because it interferes with their mineral absorption. Small amounts of diluted chlorine bleach are safe for plants and in some cases even helpful. I have used bleach on the outside house over garden beds rinsed bleach runs into soil and on plants not one fatality yet. It the only thing that kills on contact without a lot of scrubbing. Some areas I put bleach water mix in a tank sprayer designed for bleach spray ahead of time a let soak then power wash no scrubbing. Walls not so easy I prefer a gas power washer with 1300-1600 psi.gets the job done in no time. Every year in Oregon the roof has to be power washed. Maybe it would be easier to just paint my house moss green! Hehe.
Moss and green slime in my neck of the woods is a four letter word! It grows on anything .... except the cement water fountains that I have tried to get moss to grow on for years even added a buttermilk coating to encourage growth. It's all in the eye a the beholder.

I know Bumplbea there were opponents and proponents of bleach. The questions seemed to lie in the fact that the bleach combined in some chemical manner to rigid polycarbonate to produce a toxic compound that could harm people.
I don't have to scrub the Physan off, once it kills the algae the algae just washes off. I think everyone should use what works best for them in their conditions.

I would be reluctant to use bleach in any strength on polycarbonate. Everything I have read about polycarbonate says to use only a mild soap solution and a soft brush which I do in the Spring...although I don't think a power washer would harm it if done correctly.

Bumplbea, is your greenhouse glazed with polycarbonate?

My bottle of Physan arrived yesterday afternoon. Now, I'm armed!

Here is my result. Before/after. Sprayed it on, let it sit 24 hours, rinsed it off with power wash. Did the entire interior, looks great! Now have to find time to do the outside!

That's quite a difference Gina.