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Old 03-06-2016, 08:12 PM   #1
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Converting Freshwater 125 gal tank to Saltwater Tank

Hi all,

The hubby and I currently have a 125 gallon freshwater fish tank and are looking to convert it to a saltwater fish tank. When we bought the tank it was fully set-up for a freshwater system. We wanted a saltwater set-up but figured we would start with a freshwater system as we were told it was easier to manage. We have had the freshwater fish-tank for about 2 years. We had an assortment of fish and about a year ago we introduced an electric blue crayfish that ever since has managed to eat every single fish that we had in the tank. Yesterday, I bought a 20 gallon tank just for the crayfish. Which now allows us to convert our tank to saltwater. Which I am very excited about ☺

Freshwater set up
125 gallon fish tank
About 160 lbs of Instant Aquarium Tahitian Moon Sand (About 2”)
Eheim Professional 3 External Filter 2080
Undersand jet system with 8 heads
2 Submersible pond pumps
Texas Holy Rock

Last night after we transferred the crayfish to his new home. We went ahead and took everything out of the tank and cleaned it in a 9:1 water:bleach solution. Drained all the water and transferred the sand to bags. Scrubbed all the algae and bacteria off the wall of the tank with the water and bleach solution and washed the tank. Currently air drying.

I have a few questions and need some guidance into how to convert our tank to saltwater.

1.) I am planning on doing a deep sand bed. Am I able to use the Instant Aquarium Tahitian Moon Sand that I used in my Freshwater tank? I know they recommend aragonite sand for saltwater, is this that kind of sand? Are there any actions I have to do to make it ready for the saltwater tank. There is a lot of poop/debris/ fish bones currently in the 160 lbs of moon sand. I also have it outside drying, does this make it non-live? Will I have to treat it with some solution if I do use the moon sand?


2.) Can you guys also recommend a good protein skimmer for a 125 gal tank as well as power heads, reverse osmosis water filer/

Thanks in advance ☺

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Old 03-06-2016, 08:30 PM   #2
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I never recommend reusing sand. Brings in so many issues in the long run.
That sand will work, using aragonite sand is best but it isn't necessary. You can even use pool filter sand. Sands that have more silicates in them will simply mean to larger and longer diatom outbreaks.

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Old 03-06-2016, 08:32 PM   #3
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Converting Freshwater 125 gal tank to Saltwater Tank

Trash that sand. It won't work for Sw. You want aragonite based sand to buffer the water. You will also need live or dry rock. About a lb per gallon.

Why do you want a deep sand bed? Unless you want like jawfish or engineer gobies a 1.5-2" sand bed should work fine. I'd look into drilling the tank for an overflow or getting an overflow box and running a dump system. That way you can hide equipment and get an appropriate skimmer. I'm not sure of any hob skimmers that are big enough or work properly for that size tank

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Old 03-06-2016, 08:49 PM   #4
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Sniperhank, Thanks for the quick reply! I thought the same but figured it wouldn't hurt to ask. So I am guessing selling the sand on craiglist is also out of the option? Seems like such as waste to toss 160lbs of sand.

Bribo12, I did some reacher before and it seems like a deep sand bed is a lot less maintenance than shallow sand beds because it actually acts as a filtration system as the organisms that form will help remove toxic nitrates. I do plan on putting about 125lbs of live rock to start and may go up to 250lbs. As for the protein skimmers I was thinking 2-65 gallon ones would work but I am so new to this and thats why I am asking. I read that sump systems are optional so I do not know much about them. How do they work and what would I need to get that setup?
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Old 03-07-2016, 05:04 PM   #5
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since you used a bleach solution just as a safty precaution wipe it out one more time with white vinegar, This will remove any film the bleach may have left behind .

Like Hank said pool sand or play sand are the 2 best choices to help cut cost just be sure it's not too fine or you will have lots of snow storms ,

As for skimmers I just replaced a old worn out skimmer with a reef octopus and I couldn't be happier with it's performance.

As for depth of sand I wouldn't go any more than 3 inch anything more just calls out for trouble.

hydor koralia wave maker/power-head is what I use with avoid any of those cheaper brands as they are junk .

RO/DI filter is a good investment to look into .

Are you planing on adding in a sump if so I would go with either 30g or 40g , the bigger the better as you can add your skimmer and heater

A lot of the equipment you need you can find on CL just be sure its not worn out .
best way to know is plug in the equipment to see if it runs , I also suggest you pull out the propellers to see if the shafts are worn out or on there last leg . This is what your looking for on the shaft , if any of them look like this avoid that piece of equipment . they will not only make lots of noise they can also fail .

Looking forward to seeing your set up once it's up and running ,
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Old 03-12-2016, 12:29 PM   #6
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Look up sumpless tanks that what I'm aiming at on my build not unless you want to hide your equipment then you can go with a sump

Going for an octopus BH 1000 and found a guy on craigslist selling sand for .50 lbs also has $2lbs cured rock for sale as well

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