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Converting a saltwater tank to fresh


DLBELL1969
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I'm picking up a used saltwater tank and setting it up as a freshwater system. I am planning on useing the coarse sand substrate that's already in it.

Is there anything significant I should be aware of or do besides doing a good rinsing and cleaning of the tank and substrate?

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I have gone back and forth before between a FOWLR freshwater. I just washed the tank/sump multiple times (3 or 4 times) with warm and then cold tap water before finally setting it up.

 

The only thing that would concern me would be the substrate. Depending on what was kept in it before, there could possibly be a large amount of organic matter in the sand that could affect the water chemistry. I have reused some crushed coral that was previously in a saltwater tank but i did wash it quite well, and then only used a pound or two in a sump, not 60 or 80 pounds of it.

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You're definitely going to want to rinse the heck out of it if you're set on using it, substrates tend to accumulate detritus over time, plus it may be full of marine life (or dead marine critters at this point) and release a lot of ammonia as it decomposes. It's also possible that the substrate is crushed coral, or something similar that would be used to buffer a saltwater system, and that would end up raising your PH, which unless you are keeping rift lake cichlids, or have really soft water, you probably don't want. If you want to consider new sand substrate, I use pool filter sand that I buy in 50 pound bags from ACE hardware for relatively cheap for my aquarium sand substrate.

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Also, since I assume you'll need to cycle the tank for freshwater, you'll want to make sure to test for ammonia, nitrite, and nitrate levels, which if your sand is a nutrient source from detritus and decomposing things, could be quite high at first. Water changes may bring it down over time, or it may not. If you were going to setup a saltwater system, I would 100% suggest new substrate, as saltwater systems tend to be a lot more nutrient sensitive that our planted freshwater systems.

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16 hours ago, ererer said:

Also, since I assume you'll need to cycle the tank for freshwater, you'll want to make sure to test for ammonia, nitrite, and nitrate levels, which if your sand is a nutrient source from detritus and decomposing things, could be quite high at first. Water changes may bring it down over time, or it may not. If you were going to setup a saltwater system, I would 100% suggest new substrate, as saltwater systems tend to be a lot more nutrient sensitive that our planted freshwater systems.

I also got a Fluval 305 canister filter with this setup. I've washed and rinsed the sponges and boiled the biological media. Do you feel this to be sufficient to reuse or would you just buy new sponges and meida?

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4 minutes ago, DLBELL1969 said:

I also got a Fluval 305 canister filter with this setup. I've washed and rinsed the sponges and boiled the biological media. Do you feel this to be sufficient to reuse or would you just buy new sponges and meida?

I should think that you should be fine to reuse the sponges. What sort of biological media? If it's rock rubble or something that's made of calcium carbonate, you could run into an issue with it raising the ph levels.

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I started the cleaned out fluval 306 on my existing tank lastnight. I have it and my HOB filter runing on the sane tank.. I'm estimating 2 or 3 weeks before I will be ready to start the new tank an I'm thinking I can build up bacteria in the media and help jump start the new tank cycle by switching it over when I'm ready. 

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