To rock or not to rock

[Jagsfan]

Planning out my pond build and originally I thought to put rocks on the bottom to help it look more natural. Then I thought "why do that, fish gunk will just get trapped in the gravel and cause issues over time" seeing that the pond wont have multiple levels and will just be 3' deep with straight walls down, might as well leave the bottom bare as well. I just watched a video and somebody said that rocks on the bottom will block the sunlight and prevent UV rays from making the liner weak over time. I never thought of that and now am wondering if i should rethink the bare bottom approach. (Side note, even if i go bare bottom, i still plan to build a couple fish caves out of larger rocks, i just wont put gravel covering the bottom). Am I overthinking this, like every other aspect of this build, haha. Or does one have a clear advantage over the other.

 

[combatwombat]

Better to overthink it now than after it's built, I say.

Rocks on the bottom is probably the biggest debate you'll ever encounter with no clear answer. If goal of the pond is to be a house for koi, pretty much any koi keeper will tell you, "never put gravel in the pond."

If the aesthetics of the pond itself matter to you and the fish are just part of that system, gravel all the way.

If you do go bare liner, I'd install a bottom drain for sure. Will make keeping the liner tidy way easier. Will the sun break down the liner faster? Probably. But you'll still likely get decades of service out of it. And you also won't have much to move out of the way when it's time to replace it.

If you go with gravel, I would think about how you can keep things moving down at the bottom so that stuff that sinks won't get much chance to settle and that there's enough oxygen down there for bacteria to eat it up if it does. I would also try to dial in your skimmer so that nothing that falls on the pond gets a chance to even make it down there in the first place.

 

[Jagsfan]

@combatwombat Thanks for the response. So if i can still get 10-15 years out of the liner, i think bare bottom is better for me. Half the pond will get direct sunlight for about 3-4 hours a day, while the other half never gets direct sunlight. Its not like its gonna get pounded by UV's all day. Unfortunately im not installing a bottom drain or a skimmer. The pond will only be about 500 gallons, 5x9x3 and with the space restraints i have around it, i dont think i can fit it all in. Im getting a filter that is "rated" for 4500 gallons though. i know from fish keeping that bigger is almost always better when it comes to filtration. I can also put a power head at the bottom of the pond if necessary to keep that water moving.

 

[combatwombat]

Got it. At that size, I think cleaning manually shouldn't be much of a chore.

 

[BKHpondcritters]

I'm just going to go on record here & say that I've been ponding for almost 20 years (first pond installed in 2002) and I have had gravel on the bottom of both that pond, as well as my current pond (new house, new state, pond fired up Sept. 2012)

In my experience, if you have an inch or two of gravel covering the liner you will NOT have a "build up of gunk". Yes, you will occasionally have to use a net & scoop up fallen debris (leaves, etc...) but there is no significant crud that lingers in the gravel bottom. On the flip side - the gravel bottom offers an enormous surface area for beneficial bacteria to colonize (in essence, turning your entire pond into a 'biofilter')

I do have koi, though, that tend to love rooting around in the gravel & continually stir up any potential 'muck' that might accumulate. I prefer the look of a gravel bottom, as well as the non-slip surface to walk on, over an algae covered bare liner. But, that's me. Pond keeping is a very personal experience and your mileage may (and most likely will) vary.

 

[Lisak1]

I'm with @BKHpondcritters - love my gravel bottom pond, for all the reasons mentioned. And my experience is the same with any kind of build up - there is none!

 

[Jagsfan]

well crap! now im leaning back towards gravel on the bottom haha. The sides of the pond wont have rocks except for at the waterline though. Do you think it would look weird with gravel bottom and bare sides?

 

[brokensword]

relative to liner decay, realize, it will be mere weeks before algae covers every inch of underwater surfaces, including any bare liner. So, I'd not worry in that regard. I used to have a bare bottom pond but when I got into koi, because they like to root naturally, I put a thin layer of pea gravel on the bottom. The 'look' will only be initially as the algae will eventually cover everything. That said, I like the view (on my underwater cam) better with some larger rocks on the bottom, but that's more for me than the fish.

 

[cas]

I didn't rock my pond back in 2004 because it was one way to save money. I think a rocked bottom pond is very pretty, but with the algae in the spring and the plants later in the year, I don't miss it. I tried to find a picture of the pond where you could see the liner. The first picture is early in the spring just as the pump was turned on. The second picture is what it looks like when the plants take off.

 

[addy1]

Naked bottom with trap door snails and some hornwort growing, about 5 foot deep

 

[BKHpondcritters]

Again, I think it's a personal preference thing, but... I can absolutely see the gravel on my pond's bottom. Yes, it gets a bit discolored over time, but it's not covered in algae or whatever.

This is in an area about 2' deep. Not only can I see the gravel, I can see a fold/wrinkle in the liner that the gravel isn't covering because the fish have 'rearranged' it. (I need to get in there & move it back! lol)

 

[Lisak1]

Algae won't cover gravel on the bottom of the pond. My pond is completely rocked - all the rocks are carpeted with algae. The gravel is as clean as the day we put it in the pond. I used to credit our big koi for that, but we only have one now, so perhaps it's the amount of bacteria that is able to colonize the gravel? No clue, but here's a picture of the bottom of our pond - never been cleaned, looking straight down, just over three feet deep. This is from 2019, so the pond was 7 years old at this point:

 

[Jagsfan]

Thanks to everybody for the pics and experience, it helps a bunch.

 

[brokensword]

Algae won't cover gravel on the bottom of the pond. My pond is completely rocked - all the rocks are carpeted with algae. The gravel is as clean as the day we put it in the pond. I used to credit our big koi for that, but we only have one now, so perhaps it's the amount of bacteria that is able to colonize the gravel? No clue, but here's a picture of the bottom of our pond - never been cleaned, looking straight down, just over three feet deep. This is from 2019, so the pond was 7 years old at this point:

View attachment 139420

that's a great pic of the bottom of a gravel pond, Lisa; we're going to have to bookmark this for future reference!

 

[j.w]

It's just a personal choice. I did it to my bathtub pond, didn't like it so won't do it again w/any of my ponds. Others seem to be able to do it and keep things looking great. Take a chance, you only live once but LOL, you might have many ponds especially if you stick around here long enough