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Title: Rock bottom pond
Description: removing the rocks

anitapond - October 4, 2009 05:18 PM (GMT)
Well, everytime I turn around I am hearing that stones on the bottom of a pond are a bad idea. So, I am seriously considering removing the stones and rocks covering the bottom and sides of my pond. It's a HUGE project, one that I am not looking forward to, but I think the end result will be worth it. Thank goodness my pond is small!

Here come the questions:

When is the best time of year to do this and why?

What should I do with my fish?

I have a plant shelf covered with stones too. The plant shelf is about 8" deep. Should I also remove those stones?

Any volunteers to help? hahahahaha

Any advice, suggestions, tricks of the trade are much appreciated!

whisper - October 4, 2009 08:10 PM (GMT)
Where did you hear that rocks are bad? I have stones in the bottom of my pond and the fish love digging in them looking for blood worms. Are yours flat rocks or are they stones. I have a lined pond and have never had any problems. :shrug:

Its Just Don - October 5, 2009 02:04 PM (GMT)
It's interesting how, when pond builders/owners have a successful pond, they believe they have found the way that all ponds should be built and operated. The reality is that there is no one absolutely correct way to build a pond or to operate a pond. Ponds are not designed, built and operated under exactly the same parameters. What works in one pond may not work in another. There are just too many variables involved. People find what works for them and then espouse to convince everyone else that they have found the "truth" about ponds. Then the debate begins, because others have found a different way. That's so true about rocks and gravel in ponds. There are people who insist that a rock bottom provides surface area for beneficial bacteria and are good for ponds. Then there are people who insist that rocks on the bottom only provide a breeding place for anaerobic bacteria and other sordid creatures. They argue that muck will build up between the rocks, become deficient in oxygen and create an unhealthy environment.

The fact is that rocks can, and will, do both, depending upon all the other variables of the pond design and operation. Let's look at some of those variables:

Size of the pond. Ponds vary in both volume and surface area. The volume of water in the pond affects how easy it is to maintain water parameters and the number of inhabitants it can support. Surface area affects gas exchange, evaporation and thermal stability. In a very small pond, rocks can take up valuable space, reducing the volume and making it harder to maintain stable pH and the like. Rocks, however, serve as a thermal mass, storing heat and helping to slow rapid temperatures changes. In a large pond, the space taken by rocks becomes relatively insignificant as well as their contribution to thermal storage. So, size matters when considering rocks in the pond.

Filtration/Circulation The amount and quality of these two factors are so variable from pond to pond as to be sources of debate in and of themselves. A stagnant pond is going to have more mulm settle between rock spaces and accumulate on the bottom. Water at the bottom will become oxygen deficient, creating anaerobic conditions. A pond where water circulates from the bottom, as well as across the surface, will not accumulate a large amount of mulm and oxygen will be replenished. Circulation with only a skimmer system will be sufficient in a small, shallow pond, but will not suffice in a large, deep pond. That's why in deeper ponds it is usually recommended to have a drain that pulls water from the bottom of the pond. An alternative to a bottom drain in deeper ponds is an aeration stone to creater circulation from the deeper areas. How well is the circulated water being filtered? Is there a large enough filter system, both mechanical and biological, to keep organic sediment from accumulating beyond a manageable level? In my own pond, my pump is in a deep pit and the organic material settles out in that pit, where it can be easily removed from time to time instead of settling out in the pond proper. Both filtration and circulation affect whether bottom rocks are good or bad.

Pond Inhabitants The more fish, the greater the amount of waste. No two ponds have the same number, size and species of fish. A rock-bottomed pond that works well with one or two fish may not work well with a dozen. This depends upon all the other parameters as well.

Pond Location In a warm climate, the pond runs year-round. In a colder climate, the conditions in the pond change dramatically, especially when ice covers it. In those areas, rocks on the bottom may work well in the summer and not so well in the winter. Again, it depends on all the other parameters.

There are any number of other considerations that will affect whether rocks are good or bad. For example, there may be tremendous differences in what works and what doesn't work based upon the size of the rocks themselves. There is a big difference in how gravel, pebbles, rocks and boulders will function.

The bottom line is, what works for you? If your water is clear, your fish healthy and water parameters are relatively stable, "don't fix what ain't broke". On the other hand, if your water is never clear, it emits foul odors and fish are gasping at the surface or floating belly-up, then you need to reevaluate your rock situation. Then again, you should reevaluate all the other variables as well. Rocks are neither good nor bad. It depends on everything else that is characteristic of your pond. What works for me might not work for you and vice versa. My advice would be, if what you have now is not a problem, leave it alone. You could end up creating new problems by disturbing what you currently have.


tlc - October 5, 2009 04:08 PM (GMT)
Here is what I think...

I like the look of rock on the pond floor. To be honest if I didn't have such a big pond and the need to get in and out because of all the water plants, I would have seriously consider adding it. It does all the things that Whisper said and gives the pond a more natural look. The other thing that is does do is HIDE the liner and all the wrinkles. I have lots of wrinkles in my liner that I just couldn't get away from. Rocks would forsure hide all that. The downside is cleaning. I would think if the rocks were big enough they wouldn't get sucked up by the vac.

If you do decide to remove the rocks I would wait till next year IMO. I wouldn't want to stress the fish before winter sets in. Wait till late in the spring and the fish have recovered from winter. You don't have many fish do you? I would put them in one of those big rubbermaid tubs while your removing the rock if you think you need to (have fun catching them ;)). Add an airstone and a quickie filter if they are going to be in the container for a while. If your going to take out all the rock then take it all out. You can add the stone back on your rock shelf later if you want. After all you have tons of spare time :wacko:

Btw, I would vote to leave it as DP says, if it ain't broke don't fix it.


Christina - October 5, 2009 06:22 PM (GMT)
We started out with a liner on the bottom and its working fine. But those little stinkers insist on tearing out all the rocks from the plants and "creating" a rock lined pond. I can't fathom how they move rocks that are bigger than they are but they do it. Couple times a year when the pond is warm enough for the DH to get in he just takes a broom and dustpan and scoops up most of the bigger stuff so that I can replenish the rock in the pots the plants are in.

anitapond - October 7, 2009 10:58 PM (GMT)
Thanks for the insight, everyone. I agree, if "it's not broke, don't fix it" - especially if it means a lot of hard, heavy work!!! :D However, from what I understand, the mulm and anaerobic conditions develop over time. I can't keep from thinking I've just been "lucky" so far as my pond is just over a year old. What if it "breaks" when it's 3 years old? Wouldn't it be better to take care of it now before the fish start dying?

Its Just Don - October 8, 2009 12:26 AM (GMT)
It should be easy to see if mulm is building up to unacceptable levels. My pond is up to 4 feet deep and I can see how much "junk" is on the bottom. If it starts to build to levels that start to bury the rocks, then it's time to start a regimen of vacuuming the stuff out. My bet is that just isn't going to happen. You probably have plenty of circulation that is removing what would normally settle out and it is being trapped in your filter system. That's the way it should work. You could also increase the circulation by adding a bigger pump to move more water. Where there is a current, there will be no settlling out.


frogman3 - October 8, 2009 03:05 AM (GMT)
Along those lines I learned last winter to not use a net with too large of mesh since too many small leaves found there way through the nets that I used on my smaller ponds. Today I ordered two nets with a 3/8" mesh for a total of $25.00.
Well worth the investment seeing next spring I will have far fewer leaves decomposing on the bottom of the pond. As Don stated everyones pond is different but one factor that really helps your water quality is removing as many leaves in the fall before winter sets in and earily spring. And most important a earily spring water change of 20%. We are running a closed water system with the only additional water being added by mother nature. With our filtering systems not running or functiong at very low levels and the fish at their weakest its a good policy. JMO

tlc - October 8, 2009 03:38 PM (GMT)
Good point Froggy.

Now here is a redneck idea and don't laugh.

I was thinking that if too much mulm built up around the rocks you should remove the fish and probably the plants if needed, then take an air hose that's hooked up to an air compressor and blow the crap out of the mulm. Turn the compressor down to a low volume and gradually work your pressure up to where it seems to be working well without spraying water all over the place. It would stir things up so you could pump out the dirty water or use your pond vac to vacuum up the dirty water. You would be doing a big water change if you did it this way though.

Ok, now you can laugh :lol:

I just thought of this one. :faint: Do the same as above but when you pump out your dirty water you could just run it through a filter/bucket(with a hole in it) that is full of batting that would catch all the junk and then return the water back to the pond.


anitapond - October 10, 2009 12:39 PM (GMT)
Thanks, ponders! I think I'll leave the rocks in and watch the bottom like DP said. I really didn't want to do all of that work anyway! :D

I'm pretty sure my pump is strong enough (rated at 2500 gph), and I have a fine mesh net to scoop the leaves out like Froggy suggested. I do notice, however, when I stick my hand in the pond to move something around (a rock, plant, etc.) a lot of mulm starts floating around. Is that normal? To me it seems there's already a lot of gunk settled in the rocks, even tho they are not "buried" with the stuff.

With the wind storms we've had over the past few weeks, the pond has lots of "leaf fragments" that fell thru the netting. If the sun EVER comes out, I need to remove some of the plants and clean out some of the leaves. Even tho we've had some chilly nights, my WH and WL are still OK, so I can't get in the pond with a net right now. BTW, should I remove the WH and WL gradually? I'm not sure if I remove it all at once if it will upset the "balance."

I also noticed my bio filter is LOADED with mulm. The other day was very SCARY - when I came home from work, my pond lost so much water that the pump was VERY close to sucking air. What happened was the bioballs in the filter box shifted and blocked part of the waterfall. This resulted in the water overflowing out the back. So, anyway, while I was rearranging the bioballs in the filter, TONS of mulm went spilling into the pond making the water brown and yucky. Should I clean the filter out now or wait for spring?

frogman3 - October 10, 2009 02:52 PM (GMT)
I would not remove any floaters until they get frosted since they absorb the excess nutrients and removing them will allow string algae to start growing, unless they start causing a water dam of course.

I'm assuming you let your filter run all winter? I would clean your filter media any time you care too, if you feel they are getting clogged up but always use de chlorinated water to rinse them out.

Its Just Don - October 10, 2009 03:02 PM (GMT)
Clean your filter now. My filter gets loaded with mulm throughout the summer. That's its purpose. About every two to three weeks during the summer, I shut off the pump, pull out the filter mats, rinse them off and, using a fine net, scoop out the accumulated mulm from the bottom of the pump pit. This black, oozy stuff is terrific plant fertilizer and goes on the garden. Some people would also vacuum, but I don't. This is the stuff that also contains "good" bacteria that helps maintain balance. I believe that an absolutely pristine pond is not a healthy pond. I do a more thorough cleaning in the fall so that the pond goes into winter with little "gunk" and it doesn't accumulate much through the winter as the fish and turtles are not eating and therefore not producing much poo.

It is perfectly normal to have a certain amount of mulm. The important thing to remember is that it is not the mulm that is a problem, but TOO MUCH of it to the point that oxygen in it becomes depleted and only anaerobic bacteria (those that grow in the absence of oxygen) are present. These bacteria produce waste products that: 1. are dangerous to fish and 2. STINK. The only way to avoid mulm would be to put diapers on each of your fish and do hourly changes. :rolleyes: You'd also have to eliminate any plant material. In effect, you would have a fountain type pond with no living material. Even swimming pools, without adequate filtration, will accumulate material on the bottom from stuff that falls in the water. If you were to look at mulm that is not in an anaerobic state under a microscope, you would find a myriad of creatures living there that contribute to a balanced ecosystem. Guess I'll have to do a video of some of those creatures. If you want a pristine "pond", eliminate the fish and plants, add chlorine and bromine compounds and use a sand filter, i.e. a swimming pool that looks like a pond.

As for the Water Hyacinth and Water Lettuce, if the water isn't warm, they probably aren't adding much, if anything, to the pond except decay products. Just take them all out and compost them. Otherwise, they'll just kind of sit there and rot.

Just my opinion. Maybe others have other ideas and opinions.

DP :hi:

anitapond - October 13, 2009 10:50 PM (GMT)
DP, great info as usual. However, I am a bit confused: If the mulm inside the filter contains good bacteria, why clean it out before winter sets in? I would think you would want to keep it in the system during the harsh season?

And, I would LOVE to see a video of all the little creatures!

tlc - October 14, 2009 12:40 AM (GMT)
Sorry A I'm not DP but here goes...The bacteria will die off as the water temp drops then all the gunk will just rot/decompose. Not good.


Its Just Don - October 14, 2009 03:04 AM (GMT)
T's got it right. The good bacteria go dormant for the most part.

Again, the amount of goop in the filter is what is crucial. If the filter system is thoroughly cleaned, you're throwing out the good stuff along with the bad. You don't want all that accumulated goopy glop sitting in your filters. When it accumulates heavily, it is easy for it to go anaerobic and produce nasty chemicals and odors. Clean the filters and remove the mulm, but don't clean it "spic and span".


tlc - October 14, 2009 03:34 AM (GMT)
QUOTE (Its Just Don @ Oct 13 2009, 08:04 PM)
goopy glop

Goopy glop, is that a new ponding science term DP? ;) :lol:

DP, what do you do with your filter material after you clean it? Do you leave it in the filter or do you store it elsewhere?


Its Just Don - October 14, 2009 12:00 PM (GMT)
I don't think there's a science term that can describe the nature of that stuff. It's oily, stinky and doggone hard to get it washed off your hands. It's very much like the sludge that's left over from sewage treatment.

My filter material is Matala. If you've never used it, it is plastic and very resistant to deterioration. I just leave it in the filter and stream, since my water runs through the winter. The filter can go all winter without needing cleaned since the fish and turtles don't produce much waste then.


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