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I want to change the substrate on established tank.


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What's up community! Greetings from Austin Texas! So this is what I got, I have a 20 gallon high planted (ish) tank. When I first set this tank up as a newbie I went with a rock gravel, and to be honest with the addition of aquarium co-ops plant root tabs, I haven't cared because I've seen plenty of plant growth. But now after too many forums, and too much scrolling through Google images of tanks with black gravel, I am hooked on the look. So basically what I am asking, is what should be my steps in replacing my gravel? I currently only have one betta fish and three snails and a few amano shrimp living in the tank. I also have a spare 10 gallon tank I could use as a temporary tank. Just kind of want to get some advice from the community to make sure I don't do anything wrong and accidentally kill my fish and snails ūüė≥ I added a picture of what my tank looks like so you can see the current gravel.

As of today, July 13th these are my tank numbers: pH: 7.0 Ammonia: 0 Nitrite: 0 Nitrates: 10ppm

anyway, TIA to all who reply!


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With my 120, I took everything out of the tank and put wood, fish, and plants in a large plastic container while I took the old substrate out and replaced it. I did not have a choice, since I was moving the tank across the room and took advantage of that opportunity to change the substrate.

With a smaller tank, it might be practical to remove and replace the substrate while leaving the fish in and  just removing everything else, I have never done that.

If you stick with the same filter you should not have a problem with the cycle, but you need to monitor water quality closely after the substrate change. With the bacteria in your filter and on the other things in the aquarium, you should be fine. Your plants will also help with any ammonia/nitrite problem.

Gravel looks like corn.

I can say that because I know you are changing it.


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I would recommend netting out the inhabitants before pulling everything out. Who knows what might be under that gravel, and I know some anaerobic bacteria can take hold in denser substrates, and when you disturb the covering, it will gas your tank basically.

When you do switch it out, I recommend putting at least some of the gravel and maybe the gunk that was with it as a first, bottom layer, and then topping it/covering it with the new stuff to make sure the organics that you've built up already get transferred over. After that, give the water enough time to settle, as free floating silt/particles can bother the fishes gills, and check for ammonia to make sure nothing spikes. Hope that helps!

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@BettaBlake Hello from the Central Valley in California! 

Given that your bioload is so low with the betta, shrimp and snails in a 20 gallon, I do not think you will have much of an issue with this process as long as you keep the same filter.

I would move everything to the spare 10 gallon (the inhabitants, plants, decor you want to keep and filter) while the cloudiness from the new substrate in the 20 gallon settles.

Then I would move everything back over to the 20 gallon. 

Good luck with the process, I think your aquarium will look great with the black substrate!

Just make sure to thoroughly rinse the substrate and pour the water into the aquarium slowly so there is less cloudiness! 

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I've done this with several tanks. I have a set of 5 gallon pails used only with my aquariums and this is my step:

wash new substrate with tap water in a 5 gallon pail

split a plastic garbage bag down the middle and set it on the floor around the tank (to get drips)

siphon some water from the tank into a 5 gallon pail

put all the plants and fishes in the pail (with a sponge filter if you have one in your tank if not an air stone - or in your case neither is required.

put all decorations into a second pail (with a bit of tank water if you want optional)

partially cover the top with a magazine to discourage jumpers

shovel the substrate out with a doggy scoop into a plastic garbage bag (use a pail if you intend to keep the substrate)

put in cleaned new substrate

put in decoration

fill tank with new water

remove cholorine

make sure tank is near desired temp

put in plants in tank

put fish in tank (optionally with some old tank water)

clean up mess

have lunch (it is very important you start early enough to finish before lunch)






Edited by anewbie
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Great tank, will look good in black!  I agree with the other posters.  Move the fish, plants, decorations, and equipment (keep the filter running and don't clean it) to a combination of a spare tank, tote, or bucket with at least half the tank water (preferably 2/3) to make it easy on yourself.  Then remove the remaining water and use a Solo cup to remove all the existing substrate.  You may want to hold onto and return a single Solo cup of substrate to the tank and remove it when the new substrate is seeded.  I use Solo cups to move substrate because this will definitely scratch or break most containers I have, they go in my fish water change bucket, and they are recyclable.  Rinse the new substrate (if required) and refill the tank.

I just did this moving the same tank three times in a week replacing my 38 gal. aquarium, having the new aquarium leak all over the house (even though it passed leak testing for multiple days) and setting up the old aquarium in the basement in an emergency, and then moving everything back to the 2nd new aquarium at the original location.

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  • 1 month later...
On 8/16/2021 at 10:21 PM, Isaac M said:

@BettaBlake looks awesome! No more corn! Haha also, your amazon sword has really grown in, great job! 

Thank you! Even with the old gravel the sword did very well. Though I was using mad gravel tabs around it. Right now most leaves measure over 20 in long. Next step is planting some hairgrass ūüė¨

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