What's Knocking Over My Fountain?

[Mehitabel]

Hi all. This is an odd one!

I'm in south-west England. I have a 750L pre-formed pond with about a dozen small fish and plenty of vegetation. There's a combined filter-fountain unit which sits in the middle of the pond. (A Blagdon 5-in-1 2000) The pond's about 18" / 46cm deep and the fountain pipe extends a couple of inches above the surface.

For the last couple of years, from time to time I've found the fountain unit on its side - mercifully, still working! It's quite a chunky machine and obviously bottom-heavy. So whatever's tipping it over must be pretty forceful. I wondered at first if a badger had come for a drink and fallen in.. But there are no signs of badgers elsewhere in the garden and surely it wouldn't happen more than once..

I'm at a loss. I want to stop it happening because if the unit breaks it has to be replaced and that's seriously expensive. Not to mention the disruption to the pond system. Has anyone else had this happen? Suggestions welcome.

 

[JRS]

If there is no other noticeable disruption to the pond, I am thinking some type of air accumulation. I have had a couple of types of prefilters with foam in them that start floating eventually , have to weigh them down with rocks. Had a Laguna with the pump itself weighing it down which was not enough either.

 

[Mehitabel]

If there is no other noticeable disruption to the pond, I am thinking some type of air accumulation. I have had a couple of types of prefilters with foam in them that start floating eventually , have to weigh them down with rocks. Had a Laguna with the pump itself weighing it down which was not enough either.

Wow, I hadn't thought of anything like that! That could be it! My filter/fountain does have a foam layer. But what conditions would make it float? So I can try to avoid them. Also, I'm nervous of weighing down with rocks, for fear of interfering with the filter process..

 

[JRS]

Seems that microbubbles accumulate inside and is enough to float it. On one of my flat prefilters, I attached a layer of green Matala to the grid. Strong enough to hold up the rock but allows the water in through the sides. A different one, more of a box, had enough room to add some rocks inside to weigh it down.