Flexible PVC Pipe (solvent weld)

[Ratsima]

I may resort to algaecide if I can't find a less toxic solution.

I'd still like to understand why such a tiny amount of gunk (algae, biofilm or whatever) can clog a hose so thoroughly in the face of such a strong pump.

(I did order some from Lazada, just in case....)

[migrant]

Let us know the outcome please

[Ratsima]

I will post progress reports as I continue to deal with this.

One further thought that might interest the Fluid Dynamists amongst us.

The folks at the garden pond forums seem to universally believe that increasing the hose diameter will solve this problem. Their thinking seems to be that even if algae or biofilm (hereinafter referred to as "gunk") forms on the inside wall of the hose, a larger diameter hose will still allow sufficient water to pass through.

On the other hand, it may be that a larger hose actually exacerbates the problem. Given a constant volume of water output by the pump, the velocity of the water will decrease as the hose diameter increases and, conversely, the velocity of the water will increase as the hose diameter decreases.

Would the decreased velocity in a larger hose actually permit more formation of gunk on the hose walls and an increased velocity in a smaller hose tend to discourage the adherence of gunk on the hose walls? Or does the water velocity not matter when it comes to gunk formation?

[Scout]

In my experience, the green hose in your picture, with the ribs running the length of the hose is very prone to kinking. My guess is that it is kinking where it does the 90 degree bend until it is nearly closed off. Then a small amount of sludge is collecting at this pinch point until the flow volume noticeably decreases. Try replacing this green hose with the blue flexible pvc garden hose which is much less prone to kinking, my guess is this will solve your problem.

[Ratsima]

I can easily test that by having the hose drape over the side of the pond instead of going through the PVC with the 90º bend. I will try that today.

Thank you for the suggestion. (And, why didn't I think of that?)

[Ratsima]

https://www.lazada.co.th/products/takar ... 02991.html

Is this what you had in mind or something different?

[Nereus]

In theory a bigger diameter hose will reduce the flow rate and pressure, but it depends on the pump. If a simple centrifugal type of pump the increase in volume will result in a decrease in pressure, but as the pump is doing more "work" to move the increase in volume, it will soon reach a limit of how much volume it can move. Do you know what type of pump it is?
If it is some type of positive displacement pump, such as a rubber diaphragm, then just the pressure will be affected, not so much the flow.

A bigger diameter hose will also reduce the water turbulence and friction drag on the inside surface of the hose. That may not be a good thing, given what you are quoting about the buildup, although of course, it will take longer to deposit the gunk and start blocking the hose.

But the deposit rate will also be much affected by what the material is lining the inside of the hose. A smoother lining MAY result in a better flow, but increase the deposit rate, whereas a rough bore MAY cause more turbulence tending to stop the gunk depositing and moving it along. Too many variables to say one way or the other.

In industrial types of installations where there is a similar problem, the solution is to prevent what ever is causing the problem by using some type of filter on the suction side of the pump, and thereby keep the gunk completely away from the circulating pump.

Even a small "settling" pond or container in the suction line may be enough, but may require an additional small pump just used to pull the water from the pond, and then take the circulating pump suction from near the top of whatever the filter trap is.

It would be advantageous to have that slimy gunk tested to see exactly what it is. It may turn out to be a simple matter of removing the source that is producing what ever it is, even just the pH of the water.

[Dannie Boy]

https://www.lazada.co.th/products/takar ... 02991.html

Is this what you had in mind or something different?

Nearly all of the Thai hardware stores will stock it in various diameters and they will sell it by the metre so you only need to buy what you need.

[Ratsima]

In theory a bigger diameter hose will reduce the flow rate and pressure, but it depends on the pump. ...

It would be advantageous to have that slimy gunk tested to see exactly what it is. It may turn out to be a simple matter of removing the source that is producing what ever it is, even just the pH of the water.

Thanks for the detailed analysis. As your post points out, there are too many variables to pinpoint either the cause or the solution.

The pump is this one: Atman AX-5000 SERVO BRUSHLESS PUMP 5,000 L/H

I don't think I can have the gunk analyzed. IMHO, the best guess is some sort of biofilm. When I read biofilms described this most closely matches what is in my pump hose. The odd thing is that most pond owners who report biofilm problems report that it gets all over their pond; on the surface and elsewhere. The only place I've seen it is in the stuff that comes out of the hose when I ream it.

I was advised to get rid of a certain floating plant (Pistia) I had in the pond because the guppies feed on on its roots and the resulting organic waste of unconsumed Pistia root is what feeds the biofilm. I did get rid of the Pistia about seven years ago. It seemed to help at first, but now I'm right back where I started.

I strongly resist the idea of putting a pre-filter on the pump. I had that in a previous pond (on Saipan), but that proved to be way more trouble than it was worth. Since my pond is always crystal clear and almost always algae free, I just don't think that a filter is the answer. At least not one that I'm willing to consider.

(When I first moved in to this neighborhood, about five of my neighbors also installed ponds. All of them had pre-filters on the pumps. Every one of those ponds is gone now, mainly because filter maintenance was too much of a hassle.)

[laser]

The biofilm build-up in the hose does not reduce the effective internal diameter much.
A 1 - 2 mm reduction of the about 16 mm "clean" hose diameter after biofilm build-up, the resulting extra head (pressure) drop is around a few cm, for the given pump specs and some assumptions.
That effect is negligible, hence I think that the likely cause of the problem is hose kinking, as suggested by Scout earlier.
Nereus gave you a link to steel spiral reinforced hoses that solve the problem. Even the 5/8" hose seems to work (with no kinking) so that size or 3/4" should be suitable, despite the much larger 1.5" pump connection.

[hin]

Some people with swimming pools who do their own maintenance know about green algae and black algae. What you show oozing off the spoon looks like the black one. Since you have a captive water containment it can be similar to a swimming pool except far the vegetation. And you possibly have very small volume so maybe a simple experiment can be to borrow a PH test kit from somone who has a pool, or buy one as they are not expensive, and it your water is not neutral, getting it there with a bit of baling soda or acid might be worth a try. Slightly acidic should be best and possibly ok for the guppies if you don’t shock them by doing it too fast. You can get acid from anyone who does pool maintenance and it takes very little but be careful with that stuff…!

Some types of black algae can grow faster in the absence of light - like, in tank farms it can grow really fast at the fuel/water interface in the bottom of fuel or diesel tanks that have not been treated with biocide and once in the system it is difficult to eradicate.

As a point of interest, doubling the diameter of a pipe quadruples the volume. Reducing diameter to one half = one quarter the volume. So with ½” hose it does not take much restriction to greatly reduce the flow.

[VincentD]

Once the algae takes hold in the hose, it forms sheets that dislodge when the flow starts; this sheet is the thing that clogs the fountain outlet. I have had this problem every time I used the garden hose to connect to my high pressure washer. Once the algae is established, it won't go away.
You have a couple of choices.
1. Change the hose every couple of months. Make sure you clean the inlet nozzle that you connect the hose to if you have one to make sure it is algae free from the start.
2. Disconnect the fountain from the main line and just use a solar-powered one. It'll run only during the day, but will you really notice it at night?
3. If you worry about the fish, get a seperate aquarium aerator pump. I don't think the water flow alone would introduce enough oxygen, but that's my opinion.
Don't bother with varying diameters or hoses, the problem is the algae.
I got around my problem by using a seperate dedicated hose connected to the pressure washer. It is always disconnected and drained after each use.

[PeteC]

I've seen some algae "free" hoses on Lazada or elsewhere here. I imagine they must be treated with something to kill it, or a coating to keep it from forming?

[PeteC]

Re above I've looked further and they're not here, they were USA garden supply sites, although even those don't say how they are algae proof. Could all be an advertising exaggeration .

[Gregjam]

Just to throw a cat amongst the pigeons. How about trying out a smaller diameter hose! It would reduce the kink inside the pipe as it negotiates the ninety degree bend hopefully and the increased flow/pressure might dislodge any algae buildup.
One of the most interesting threads running at the moment however unintentional.