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Changing a substrate

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Once you have the concept sorted, look at the plants/wood/decor you want to use. Where will the go? Research the "Golden Rule" or the "Rule of thirds" as a basis of your 'scape. Choose plants to suit as well. When buying plants, consider that you may need them a few days beforehand so you can wash them and free them of pesticides before adding them to the tank. Any new decor should be washed. When buying wood, consider that it may need weeks of soaking and/or boiling to remove tanins or to get it to sink - sinking can be encouraged by attaching a stone to the wood. Do consider the effect on the water chemistry of your new substrate - coral sands and gravels will increase hardness and pH.

So, you've bought everything you need, and you're armed with your concept. Decide on the day you're going to do the big change. Before you even go near the tank, prepare your new substrate(s), wash thoroughly where applicable, and place in to a convenient container. Have the wood and the plants ready to go, and easily accessible. They key to you substrate change days is having everything cleaned, washed and prepared and laid out for easy access.

Done all that? Everything prepared? This is key. You will be removing fish from the tank, and once you do that, your priority is to have them out for the least time possible.

So, what to do with your fish? Get a tub or tubs that can accommodate your fish. You can get 80l tubs for under £10 from Wilkos or Tesco. If you can keep them together it will make life easier.

In your tub it is wise to have an airstone and some plants. You will also need to be able to darken the tub - a towel will do. Consider filtration and heating. A warm room may mean there is no need to heat the water. Filtration - smaller internals can go in the tub, but consider the effects on the fish. Filter media near the air stone will be suitable if a filter isn't practical. Filter media needs to be kept wet regardless.

Now, double check you're good to go. Drain tank water in to the tub so the fish can still swim. Take out decor and plants to facilitate netting the fish. Get the fish in to the box, lid it and darken it. Next, drain some more water to save either in the tubs or a bucket, but before you drain the water completely, scoop out the old substrate completely. Then drain the rest of the water - if you've had gravel, there will be plenty of muck to remove! Try to remove all the water and muck as you can, but it's not the end of the world if you can't or don't. When it is all out, start laying your new substrate. Add the hardscape, rocks, wood, ornaments etc. Next put 4" of water in the tank and get some plants in. Now add some of the saved tank water back in to the tank, then the fish. Finish planting, add the old tank water back, and then start finishing the taller plants, top with fresh new water as necessary.

When refilling to avoid dust being thrown up in to the water, refill on to a plate or a bag. Then back siphon the water slowly. Don't disturb the substrate.

I've done this twice now. On a 2' tank, I had the fish out for 90 minutes, the 4' took me about 4 hours of the fish out, but I had the tank to clean as well.

The fish will be fine in the box - even unfiltered. They go through far worse when being shipped, and are subjected to a bag for 12 hours or more.

When it's done, feed sparingly. Your "good bacteria" lived partly in that gravel that's gone in the bin. Because of this, you may see a mini cycle. Do what you can to manage this - less food, and possibly water changes. It shouldn't take too long if you do see a cycle start.

Big J adds: There are some bacteria in the gravel itself, removing this in one go may cause a mini-cycle. To avoid this, fill a leg from an old pair of tights (or similar) with the old gravel, and put this back in the tank, just laying on the sand. I've used this idea several times and never had a cycle, I've had friends and relatives ignore this advice and lost fish due to the mini-cycle!

Any questions, comments, suggestions, omissions and corrections welcome, we can leave this here for future people to come and read.

Very good! Can this be stickied up the top?

brill post i think the key is organisation thinking of doing this myself soon when i can afford it. had my tank up and running 14 months now want to change from gravel to sand esp for my corrys

Absolutely, plan and prepare like mad. There's usually no rush to get the job done, and doing it right, and doing it once is so much better!

Wee do you heat the water to same temp as tank and how important is this assuming it depends on how much water your changing? 

I am going to be changing substrate in my small 28l tank so wont really take to long its in the middle of a cycle and quite small so fish wont be out tank that long and assuming it will be okay just to pour most of the tank water back in? but just wondering for future reference when my bigger tank is up and running for water it okay to have similar temps i.e. judging with touch and syphon it in rather than pouring ??


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