New Substrate

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Fish Fanatic
Jul 25, 2021
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Hi again, I'm currently in the process of transferring to live plants and as such have purchased a new substrate (as well as plant fertiliser, ammonia test, new light & hardscape). I have bought a normal gravel substrate to mix with a plant substrate, more specifically Golden Tree Aqua Soil. I don't know if it contains ammonia yet or not. When replacing the substrate, do I need to cycle my tank again or will it be okay? For reference the tank has been cycled for about 3-4 months and I will be leaving the two live plants in that I currently own, but I don't have anywhere to put the fish unless I leave them in a bucket with a filter running for a night or two. No ammonia or nitrites are present.


Fish Aficionado
Oct 28, 2006
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Kent, UK
I would suggest getting some of the aquasoil and putting a good amount in a jar or bucket with some water. Leave it a couple of days and then test the ammonia. If its all clear you are probably going to be ok.

If its not all clear then life becomes a lot more difficult for a number of reasons.

1) You are replacing your current substrate which will have a lot of beneficial bacteria so reducing your biological filtration somewhat.
2) You are adding something that is potentially going to leach more ammonia then your biofiltration can cope with. Generally this will not be something that is done in a couple of days but can be going on for weeks. ADA amazonian for example can be a couple of months before it settles down, even then I think it still probably leaches ammonia, just the plants and filter can deal with it quickly.

Both of these issues can cause you to have Ammonia and Nitrite spikes which are obviously not a good thing for your fish and you are basically going to be creating a fish in cycle.

There are ways to reduce the problem though.

1) Plant really heavily (like filling the majority of the tank with some form of plant) with lots of floating plants and fast growing stem plants. These will be able to deal with the ammonia better than your biological filtration can.
2) Do lots of large water changes. Test your Ammonia and Nitrite levels, you want your water changes to be bringing these down to zero (or as close as you can possible get). It will most likely mean 50-70% water changes every day to begin with. Once your plants get established and your biological filtration grows to fit its new food supply you will be able to reduce these back down again.

Edit to add:
You don't necessarily have to use aquasoil to grow plants. I use it a lot and love it but you can get just as good results using root tabs in an inert substrate and water column ferts (either just from fish waste or adding extra yourself).

Most aquatic plants are more than capable of taking nutrients in from both the roots and the water column. Some plants do prefer root feeding but then root tabs are generally enough to keep them growing.


Moderate Moderating Moderator
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Global Moderator ⚒️
Jul 16, 2013
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Oxfordshire, UK
@xxBarneyxx has pretty much said it all.

Not much to add to that since good advice and solution are already given regarding the new substrate potential issues imho.

Only thing I may add, is perhaps get a small filter and take some of your established filter media and put this in the small filter and add that to the holding tank, this can be a large clean tub or a temporary second hand tank that can be used for your current livestock. Doing this with the filter will help deal with the bio load and remember it’s only temporary until you establish if the new substrate leaches ammonia or not.

Then take things from there, one step at a time really.

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