We originally had small rocks on the bottom of our pond. At first, they looked nice but eventually became covered with algae. Water was clear but the rocks were green. Also, we don't have a bottom drain and they made the pond difficult to clean and my potted water lilies would fall over because they were sitting on the rocks. I think the koi actually liked nosing around in the rocks but after reading so many negative things about rock bottoms, we removed them last spring. That was a back-breaking job. Pond maintenance is so much easier without them!

Like mindysue said....pond maintenance is SO much easier without them. If you do have rocks in the pond, you must completly remove them and pressure wash the pond at least once a year. And even then, rocks will harbor decaying fish food and waste, forcing your koi to live in the equivilant of a septic tank. So I guess bottom line is that there is NO safe and healthy way to include rocks in the bottom of a pond.

If you really want rocks on the bottom, just put in a thin layer of gravel, so thin you can see the liner if you move them around. The size of the rocks should be about 1 to 2 inches in diameter. Rainbow Rocks from Lowes looks good, or some other kind of river pebble. If you have a pond vac or a shop vac with a narrow nozzle, you can move this thin layer around with it to vacuum under them. Just be careful not to suck them up.

The others are correct -- there is more maintenance involved in having rocks or gravel in the bottom. But it can be done, and frequently is done in my area. PondEco Aquatic ponds are popular here.

There is more maintenance, but I don't agree with the statement that rocks on the bottom is lethal to fish. I mean, as long as you don't have a 10 inch layer of pebbles at the bottom. My pond has a very thin layer (1" or less) of rocks at the bottom just for cosmetic reasons and no old debris below it since I vacuum it monthly. I think a black, plain bottom looks too unnatural. My pond water has always tested PERFECT despite what others say about having rocks on the bottom. If you are willing to do monthly maintenance, you will be fine. Even ponds without rocks on the bottom require some sort of weekly or monthly maintenance. The fact is, fish eat and poop whether you have rocks or not. The poop gets trapped in the filters or settles on the bottom...Then bacterial degrades it. So whether you have rocks or not...I don't think there's much of a difference.

Ponds with natural bottoms - fish are ok despite mud and rocks on the bottom. Your pond will be ok with some pebbles/rocks on the bottom. Just don't go overboard.

The question weather not you can safely have rocks in the bottom of the pond. The answer is yes but not in the ways they are commonly put in unless you want a lot of work. My koi pond has about 10 inches of rock in the bottom and has never been cleaned in 15 years. There is 11,000 lbs of 3/4 inch gravel on the bottom. It has never been disturbed from the day I put it in. The rock stays as clean as the day it was installed. You are thinking either I am lying or something is going on. You see I have a series of pipes running at the bottom of the gravel bed that are 12 inches apart and lots of holes in pipes and I suck water thru these pipes. During the winter about 3000 gph and during the summer about 9000 gph. The only maintenance that has been done on this pond since last Nov has been to feed the fish three times a week The pump baskets on the skimmer pumps will need to be cleaned out in the next month but that is it. I also built a pond for a client three years ago that wanted koi and rock on the bottom. So we installed bottom drains that were level with the 4 to 5 inch rock that we lined the bottom. The rocks were mortared together to keep debri out and let the bottom drains work. The bottom for the most part stays clean and has not needed to be cleaned. But these are not the normal ways that rock on the bottom is installed. Ponds with rock on the bottom the water will test just fine unless you are testing for HS or CO2. Since most people don't test for these they don't know they have a problem.
Mike

That set up is a bottom filter which I have used for years in an aquarium set up, but I don't have that type of filtration in my pond so I have no rocks.

always_outside.....a properly designed filter does not rely on bacteria to degrade the fish poop. Filter bacteria converts ammonia into nitrates which renderer it harmless, but it does not digest fish poop. A properly designed pond has a bottom drain in it that gently moves the fish poop to a mechanical filter where it is captured so that it can be flushed from the filter. It should never be allowed to just sit in the filter forever, waiting for bacteria to digest it. My 9000 gallon pond has two bottom drains and no rocks. Pond maintenance take me maybe 15 minutes a week to keep the pond bottom spotless and the water healthy.

If rocks are in the bottom and never cleaned, hydrogen sulphide gas starts to form as the fish poop decays. These gas bubbles might never break loose....they might just stay under the rocks and never cause problems. But if a gas pocket ever does break loose, the result will be immediate death of pond inhabitants. Hydrogen sulphide gas is very deadly and it is a proven fact that it can and does form in the rocks at the bottom of most ponds with fish.