1400G outdoor koi pond / tank


New Member
Hey all, I know this is about reefs but I hope you guys (and gals) wouldn’t mind giving me advice before I screw up :) this is my first custom build tank, I have had a fresh water 60g tank doing well for almost a year…I want to build this for koi fish and yes I am in Maryland and will have a cold winter….

I think I will start with my vision.
There is a second tank on top for plants and maybe smaller fish to waterfall into main tank through a cut out in the center over that lip, with lights behind it to light up the waterfall.

Now to real photos
let’s start at the base, it’s on an 8 inch footer 10X 10. Then 2 feet all around with 4 inch cider block and 3 inches of foam on from 3 walls and back wall is 4 feet tall with 3 inches of insulation. Before I put the insulation in, I also used dryloc on the inside to seal the cement. I then put a pond liner over it, and used several types of pond tape to cut and seal the corners as well as rubber flex seal. I still don’t think it’s sealed enough I fortunatly cause I filled up tank a few inches and over night it dropped a few mm.
While I was doing that, I had acrylic walls being cut . Based on me thinking the cinderblocks were actually 4 inches think not 3.5 (or whatever they actually are)… so my math on length of side walls were off… this frustrated me ….

the initial idea, was the side walls would sit flush to the insulation….

yea that’s not going to happen now because I ended up pulling the walls 1.5 inches forward to make sure the front acrylic wall was not almost falling off the inside part of the cinderblock wall….

Instead I got huge (1/4in thick) aluminum 90 degree channels…. And sandwiched the back acrylic walls.
This in turn left a huge gap between inside acrylic wall and back cinderblock wall. Which I filled atleast the top and sides with silicone.as well as all the end seems.

I also bolted through the back cinderblock walls.

I order to mount the acrylic walls to the base , I put very thin( ) 1/2 u channels. I used cement screwes to attach them to the cement, and drilled counter sunk holes under the acrylic to fit “smoothly” over the bolts, (or to use to adjust in leveling if one side was to high / low). I bolted them in over the tarp, and put JB weld epoxy in the channel, over the cement screwes and under the walls.

on the inside back walls, I filled the gap between insulation and 90 degree metal channel with some silicone, then capped the front with a think 90 degree channel just to make it look a little nicer and added more silicone.

(pic to come)

I added epoxy under the u channel from outside just as an extra layer of protection. I also put a layer of silicone on inside wall to seal the liner to channel and another one to seal channel to acrylic…

I still need to install the plumbing at the base. And figure out what to put on outside all decoratively… and electrical. Wow this was more work then I thought.

Feedback and comments welcome!


JoePa lives on!!!
Staff member
Oh boy, I don’t even know what to say vs I’m following along! I love the above ground build, I usually see these in the ground for overwintering


New Member
After reading some posts on here and learning that silicone won’t bind to acrylic…. Boo…. I then sent mm by mm with my finger smoothing it down and in the edge of my u channel…. Vs just sliding it along like I did on the inside, it def looks nicer, but doubt will do much against water

considering you can’t even see it on the right side lol.

This was the cap that was to hide the gap behind it.


I think the corners came out amazing… just need to wait a few days for all the silicone to cure, then to test….


New Member
So had some leaks :( lol the acrylic walls didn’t properly seal at the bottom … I had to add epoxy to fill the hole.


Then I worked on the pluming, i thought I did a good job…

853FCA6B-EDEF-4A53-B6EF-AFF1ACA6B35B.jpegTurns out using JUST silicone to seal it was a horrible idea. Mainly because the pvc didn’t stick to the cement, so it spun and the silicon ripped right off and made a nice hole….

I didn’t take a picture of the inside where the hole was, but this was it leaking out the other end.

so I took it all off an started again. This time I used JB Weld putty, on the inside ring between the insulation and pvc under the liner, then used supper glue gel to stick the liner to the pvc, then put more JB weld around the outside. I am “hoping” that helps. But just to play it safe, I am going to use flex seal putty (it’s white:( )over that and the tarp, then a coat of the black flex seal.
I will update you all in a few days.