Setting up a Rubbermaid 300 gallon stock tank with underlayment and pond liner

[2bfishy2]

Hi, it has been a long time since I have posted on here. I was 2bfishy. But I couldn't remember my email address that I used for my account, so I had to create a new account with a different email address. So now I am 2bfishy2. I had a 8 foot diameter index snap set 500 gallon pool pond that housed mainly 9 sun catfish, 2 four line catfish, and various cichlids and buenas aires tetras, swordtails, and 2 oscars and a black spotted eel. I ran 3 tetra pond flat box filters totaling 1500 gallons of filtration and it was a very successful pond that I had up for 5 years.

Unfortunately, some repairs needed to be done in my basement and the pool pond was taking up a lot of space in the basement, so the repairman didn't have access to where he needed to repair, and I had to take the pool pond down. I took the fish to my local fish store and have been in a major funk ever since. That pond was my happy place and I really miss it. Fast forward a month later and I have gone to that same fish store every weekend for the last 4 weeks. This last week I saw they still have four of my adult sun catfish and 1 four line catfish left. They had them all housed in a 75 gallon tank. I feel really bad for them because they were in my 500 gallon pool pond their whole lives until now. I was determined to get them out of there. So I bought a Rubbermaid 300 gallon stock tank and put it in my basement on an insulated foam pad. I have read on various forums that these stock tanks tend to get cracks and leak so I didn't want to risk it and have bought a combination underlayment and 45 mil EPDM pond liner off of Amazon that arrived today.

Unfortunately, I have no experience with pond liners, only pool ponds, so I need some guidance on how this is done.

Do I just lay down the underlayment in the 300 gallon stock tank and lay the pond liner over it? I will be heating the tank with a room heater. Should I put any kind of insulation under the underlayment first to insulate it better in case of power outages?

 

[tlindsey]

Hi, it has been a long time since I have posted on here. I was 2bfishy. But I couldn't remember my email address that I used for my account, so I had to create a new account with a different email address. So now I am 2bfishy2. I had a 8 foot diameter index snap set 500 gallon pool pond that housed mainly 9 sun catfish, 2 four line catfish, and various cichlids and buenas aires tetras, swordtails, and 2 oscars and a black spotted eel. I ran 3 tetra pond flat box filters totaling 1500 gallons of filtration and it was a very successful pond that I had up for 5 years.

Unfortunately, some repairs needed to be done in my basement and the pool pond was taking up a lot of space in the basement, so the repairman didn't have access to where he needed to repair, and I had to take the pool pond down. I took the fish to my local fish store and have been in a major funk ever since. That pond was my happy place and I really miss it. Fast forward a month later and I have gone to that same fish store every weekend for the last 4 weeks. This last week I saw they still have four of my adult sun catfish and 1 four line catfish left. They had them all housed in a 75 gallon tank. I feel really bad for them because they were in my 500 gallon pool pond their whole lives until now. I was determined to get them out of there. So I bought a Rubbermaid 300 gallon stock tank and put it in my basement on an insulated foam pad. I have read on various forums that these stock tanks tend to get cracks and leak so I didn't want to risk it and have bought a combination underlayment and 45 mil EPDM pond liner off of Amazon that arrived today.

Unfortunately, I have no experience with pond liners, only pool ponds, so I need some guidance on how this is done.

Do I just lay down the underlayment in the 300 gallon stock tank and lay the pond liner over it? I will be heating the tank with a room heater. Should I put any kind of insulation under the underlayment first to insulate it better in case of power outages?

I don't have any experience with pond liner but welcome back.

 

[jjohnwm]

Wow...you have a serious case of the belt-and-suspenders syndrome, don't you?

I've seen a couple of Rubbermaid stock tanks that cracked after years of sitting in cow pastures, getting leaned on by heavy livestock, pushed around with tractors and backhoes, subjected to repeated freeze-thaw cycles, etc...in other words, fulfilling their designed purpose of providing water for big critters. But as an aquarium in your basement? Trust me, you will grow old and die long before that tank cracks...and even then it likely won't happen unless they drop you (in your coffin) on it from a height.

I have seven outdoor stock tanks now...most of which were picked up for free or dirt cheap...and none of them are Rubbermaid. Even the cheapest, flimsiest of them has never cracked or leaked. You have nothing to worry about.

I would suggest placing the stock tank on a sheet of styrofoam to insulate it from the cold basement floor. Better still, get a few concrete blocks, make a few stacks and then cut a plywood base to sit on the blocks and on which the tank will sit. The water will stay much warmer when not in contact with a cold basement floor, and it's much nicer to observe the fish when the water surface is up around waste level rather than way down low.

 

[2bfishy2]

I don't have any experience with pond liner but welcome back.

Thank you! I’m glad to be back

 

[2bfishy2]

Wow...you have a serious case of the belt-and-suspenders syndrome, don't you?

I've seen a couple of Rubbermaid stock tanks that cracked after years of sitting in cow pastures, getting leaned on by heavy livestock, pushed around with tractors and backhoes, subjected to repeated freeze-thaw cycles, etc...in other words, fulfilling their designed purpose of providing water for big critters. But as an aquarium in your basement? Trust me, you will grow old and die long before that tank cracks...and even then it likely won't happen unless they drop you (in your coffin) on it from a height.

I have seven outdoor stock tanks now...most of which were picked up for free or dirt cheap...and none of them are Rubbermaid. Even the cheapest, flimsiest of them has never cracked or leaked. You have nothing to worry about.

I would suggest placing the stock tank on a sheet of styrofoam to insulate it from the cold basement floor. Better still, get a few concrete blocks, make a few stacks and then cut a plywood base to sit on the blocks and on which the tank will sit. The water will stay much warmer when not in contact with a cold basement floor, and it's much nicer to observe the fish when the water surface is up around waste level rather than way down low.

Hi, I thought about propping it up on cinderblocks but honestly I prefer having the tank on the floor on a sheet of styrofoam for insulation like you mentioned.

 

[2bfishy2]

Also, since I tore down the pond a month ago, I will have to do a new cycle on this tank. I have a 40 gallon community fish aquarium that has two seasoned 125 gallon sponge filters for filtration. If I put one of those seasoned sponge filters in the 300 gallon stock tank will that cycle the tank faster? Will adding Seachem Stability or Seachem Safe help speed up the cycle at all?

 

[2bfishy2]

I know you think it might be overkill, but I really have heard of these Rubbermaid 300 gallon stock tanks leaking sometimes, especially around the drain plug even if people silicone the plug, use plumbers tape, etc. I have heard of those failing and still leaking overtime. And I do have the underlayment and pond liner that arrived today from Amazon so I will be using those on this stock tank. My question is how do I do this? Should I put anything under the underlayment to insulate it better?

 

[jr71]

You got me curious about this, too, so I posed your original Q to ChatGPT and got the following information:

You can lay the underlayment directly into the Rubbermaid 300-gallon stock tank, covering the entire bottom and sides, and then drape the EPDM pond liner over it. Try to smooth out any large folds, especially on the bottom, and leave several inches of liner overhanging the top rim. That overhang helps prevent slippage and gives you room to secure it if needed. The weight of the water will help press everything into place.

If the liner is quite a bit larger than the tank, you can trim it after filling, but it’s best to wait until the tank is full and the liner has settled to avoid cutting too short.

While the Rubbermaid tanks are generally reliable, using the liner adds an extra layer of protection in case of cracking or slow leaks over time, especially with temperature fluctuations in basement settings.

For insulation, adding a layer of rigid foam board (like XPS or polyiso) underneath the underlayment is a good idea. It helps reduce heat loss into the floor and can be useful during power outages. You can also wrap the outside of the tank with foam board or reflective insulation like Reflectix to retain warmth more effectively, especially if you’re heating the room rather than using an in-tank heater.

If you're concerned about power outages, keeping the tank insulated helps slow down heat loss, but also consider adding a battery-powered air pump or backup power option for aeration and circulation.

 

[2bfishy2]

You got me curious about this, too, so I posed your original Q to ChatGPT and got the following information:

You can lay the underlayment directly into the Rubbermaid 300-gallon stock tank, covering the entire bottom and sides, and then drape the EPDM pond liner over it. Try to smooth out any large folds, especially on the bottom, and leave several inches of liner overhanging the top rim. That overhang helps prevent slippage and gives you room to secure it if needed. The weight of the water will help press everything into place.

If the liner is quite a bit larger than the tank, you can trim it after filling, but it’s best to wait until the tank is full and the liner has settled to avoid cutting too short.

While the Rubbermaid tanks are generally reliable, using the liner adds an extra layer of protection in case of cracking or slow leaks over time, especially with temperature fluctuations in basement settings.

For insulation, adding a layer of rigid foam board (like XPS or polyiso) underneath the underlayment is a good idea. It helps reduce heat loss into the floor and can be useful during power outages. You can also wrap the outside of the tank with foam board or reflective insulation like Reflectix to retain warmth more effectively, especially if you’re heating the room rather than using an in-tank heater.

If you're concerned about power outages, keeping the tank insulated helps slow down heat loss, but also consider adding a battery-powered air pump or backup power option for aeration and circulation.

Awesome! Thank you for this! The foam board is that the pink foam board you are talking about? So I would lay that down in the stock tank on the bottom and then lay the underlayment down and then the pond liner?

 

[jr71]

Awesome! Thank you for this! The foam board is that the pink foam board you are talking about? So I would lay that down in the stock tank on the bottom and then lay the underlayment down and then the pond liner?

Response from AI again:

Yes, the pink foam board you’re referring to is likely extruded polystyrene (XPS) insulation — commonly sold as Foamular at Home Depot or similar brands at other stores. That’s exactly the kind of rigid foam board that works well for this application.

To clarify the layering order inside the stock tank:

1. Bottom of the tank
2. Rigid foam insulation (e.g., pink XPS board) – cut to fit the bottom as neatly as possible
3. Underlayment – lays directly over the foam and up the sides of the tank
4. EPDM pond liner – draped over the underlayment and shaped into place

The foam board helps reduce heat loss through the bottom and adds a little cushioning. If the foam fits well, it shouldn’t shift once everything’s layered and filled. Just make sure it’s clean, smooth, and free of sharp edges.

Optional: You can also insulate the outside walls of the tank with foam board or Reflectix-style wrap for even better heat retention, especially if you’re relying on ambient room heat.