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Discussion Starter · #1 ·
Hello everyone. I have a 125 gallon freshwater tank (long version) and I want to change out the substrate from stone to sand. Also, there are a couple catfish I want to remove in the process. I have quite a bit of lava rocks built up as a wall at the back of the tank. What is the best method to replace the substrate without harming the good bacteria already built up on the rocks. Are there any pitfalls to avoid?

The sand I want to use is called Tahitian Moon Sand. I've seen some folks say that this sand is toxic and have killed their fish, while others said they've had no problems. Does anyone know about this? Is there any other sand I should consider?

Also, I don't recall how much stone I have in the tank now, so what is good amount of sand to put in the tank to support lava rocks?

I'd appreciate any advice or feedback.

Thanks...Al
 

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I don't see CaribSea Tahitian Moon Sand on their website anymore unless I just couldn't find it. I did however see on another forum that there was an issue with some batches of this product that caused some fish deaths.

Are you looking specifically for a black substrate?

You will want any rocks to sit directly on the glass or acrylic bottom of the tank and NOT on the substrate as some cichlids will excavate around the base of the rocks or stones and cause them to topple.

If you are planning to completely remove existing rocks to catch fish, just turn off any filtration and use a scoop, dustpan or similar container to remove existing substrate.
 

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Changing substrate out is not easy, but not hard either. With a bit of planning, it will go smoothly.

Before touching the tank, obtain the new substrate and rinse it very, very well. Keep in buckets for now. For a 6' 150, I'd expect to need about 150lbs. That was about 3 bags of pool filter sand when I did mine.

Obtain a bunch of extra buckets to store existing gravel. I often will remove the rocks from my tanks and place them on the floor over a towel which is over a plastic sheet. Remove fish, into buckets. Drain water down to a manageable level. I've used a plastic kids sand shovel to scoop out the old substrate. Once old substrate is out, place the rocks back into the tank. Next add the sand to the tank, and level as you desire. Replace water (think of it as a huge water change), and put fish back into tank, start filter, and enjoy the new look. Plan on a couple of hours, excluding rising the new substrate.
 

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Discussion Starter · #4 ·
Thanks for the feedback. It's been awhile since I've ever done a change like this. I will be removing all the Lava Rocks, so it's best to place directly onto the glass.

Deeda, according to youtube videos, they discontinued that particular sand, so there must be some truth about the problems. And, yes I want Black sand as that's the color of my current substrate and I like the contrast with the Red Lava Rocks.

Again, thanks.
 

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For black sand, look into Black Diamond Blasting Sand sold at Tractor supply. I've used this in several planted tanks, and really like it, plus the price is right. Approx $9/50lbs. There are at least two sizes, and I'd recommend the medium over the fine.
 

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nodima said:
For black sand, look into Black Diamond Blasting Sand sold at Tractor supply. I've used this in several planted tanks, and really like it, plus the price is right. Approx $9/50lbs. There are at least two sizes, and I'd recommend the medium over the fine.
I think there are at least four sizes ... the problem is finding anyone local who stocks anything other Medium and Fine ... :D

I have the Medium in one tank here ... I'd actually prefer something coarser.
 

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Discussion Starter · #8 ·
Question. Is it necessary to remove the fish from the tank when during and substrate change out? I don't want to have to recycle my tank, nor do I want to damage the good build up on the lava rocks.

Btw, I am considering the pool filter sand to try something different in the tank as I've always had Black substrate. Any reason not to use pool filter sand?
 

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Pool filter sand is great. Removing the fish is not necessary but it is safer, faster and easier to do with them out of the tank. You will not need to recycle and just don't wash the rocks...but take them out.
 

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I have done substrate changes keeping the fish in. I believe most of the good bacteria are NOT in the water, substrate, or rocks - they are in your filter so do not turn your filter off for too long. When I did my change with fish in, I turned off the filters for 30 minutes and removed as much gravel as I could. Water got dirty/cloudy. I then turned filters back on and let water clear up and I continued 24 hours later.

Should you choose to remove fish first - again preserve the filter media - not sure how long it will survive with filter not running.
 

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The whole process should take about 2 hours (get everything ready first) so your filters will be fine not running for that period of time.
 

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Discussion Starter · #12 ·
Thanks everyone. I do plan to have everything ready to go before removing the old gravel. I will have already cleaned the new substrate, removed the stones and lava rocks and let the filter run to clear the tank before I put in the new stuff.
 

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Discussion Starter · #13 ·
punman said:
I have done substrate changes keeping the fish in. I believe most of the good bacteria are NOT in the water, substrate, or rocks - they are in your filter so do not turn your filter off for too long. When I did my change with fish in, I turned off the filters for 30 minutes and removed as much gravel as I could. Water got dirty/cloudy. I then turned filters back on and let water clear up and I continued 24 hours later.

Should you choose to remove fish first - again preserve the filter media - not sure how long it will survive with filter not running.
Punman, I see you have a Frontosa tank. Do you have any photos of you setup? I plan to do a 150 tall Frontosa setup. I love those fish.

Thanks.
 

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Discussion Starter · #14 ·
I settled on pool filter sand for several reasons: 1) I've used Black gravel for over 30 years now and wanted to try a different look, 2) the cost factor ($55 vs $200+) - unfortunately pool filter sand is not $6 where I live, 3) my ph is stable around 7.8 and according to some research, it suggest not to introduce any ph altering media (I was considering the Caribsea African Cichlid mix).

I am currently cleaning the sand now. I'm excited for the new look. It's going to be some work rebuilding the inside, but hopefully worth the effort.

Is it necessary to remove the fish in the tank? I have small fish (1.5-2").

Thanks...
 

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As punman says, it is possible to do this with the fish in the tank.
 

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Discussion Starter · #16 ·
Update: All done. I left the fish in and they seemed to enjoyed all the ruckus. I removed the 2 catfish I no longer want in the tank. Tank is all clear and a 100% different look to it now. I just need to rebuild the rock wall, but looking to get a few additions before attacking the build. The fish seem to like the sand.

Thanks everyone.
 
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