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Discussion Starter · #1 ·
I've had my tank cycling for almost 2 weeks now, and as such, some water's evaporated and it should probably be topped up. When I bought the tank, the LFS told me that they sell RODI water that's already mixed to the right salinity, and it seemed much easier to buy it from them than to mix my own at home and invest in an RO unit, so I bought 100 litres. With the live rock and sand etc, the tank actually comes down to only holding 75 litres, so I have one container of water left over, but it's just been sat in a sealed plastic container (sold by the LFS so it's clean at least) for 2 weeks with no filtration or even circulation.

Is it going to be safe to add this to my tank now to top it up, or will it have stagnated or in some way gone bad and shouldn't be added to the tank water?
 

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I've had mine in a garbage can for two months with no issues. I top off every two days and refill once a week. A unit is well worth it. I paid $175 for one from bulk reef supply
 

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No. Mixed salt water is for the initial filling and for water changes. For top off you need to use straight RO/DI or distilled water. The salt does not evaporate so if you added more saltwater the salinity would rise too high.

If it is sealed the salt water should last a month or so.
 

· Captain Obvious
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stop the presses. yeah.

there are TWO types of water most LFS sells.
1) pure RODI water, no salt, just pure water, you could drink the stuff.
2) salt mixed with RODI with a salinity at 1.02x. x being whatever they choose

IMPORTANT:
if you keep topping off with water that has a salinity of 1.02x, you will pretty quickly raise the SG in your tank to over 1.030 or higher. what evaporates in your tank over a week or so is just WATER while the salt is left behind. less water and more salt is concentrated in your SW and your salinity goes up.

you ONLY topoff with pure RODI water with NO salt mixed in there. If you do it right, by replacing the amonut of water that evaporated with RODI water you get your salinity back to where it was before the evap started.

Good you posted you question. it not stupid at all ..... as everyone on this board started soemwhere with their knowledge
 

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Discussion Starter · #5 ·
I've checked the SG in the tank with a hydrometer and it's still showing at 1.025 (same as the water in the container), surely adding 1.025 water to 1.025 won't increase the salinity? I quite appreciate and understand the point that only the water should evaporate, but the SG reading is still the same, so it shouldn't raise the SG on that basis should it?
 

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Only water evaporates from the tank, not salt. So the tank waters salinity raises as water evaporates. Adding pure water to the tank to top it off will keep the same amount of salt in your tank. If you add new salty water to increasingly more salty tank water you'll raise your salinity slowly but surely.
 

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Discussion Starter · #8 ·
Right, thanks for the advice. I'll bob down to the LFS tomorrow and get some RO freshwater then. Would this container of 25 litres of saltwater be worth keeping for water changes at least, or shall I tip it away now and not have it sat around for god knows how long until I can put fish in there?
 

· Reef Junkie
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I would invest in a refractometer. There is no way your salinity hasn't risen in two weeks with evaporation. I would also highly recommended purchasing an RO/DI unit and at least a handheld TDS meter.

Buying water is going to get very costly over the long run and you have no idea how pure the LFS water is. You're going to need salt anyway to maintain salinity so you're already going to be mixing your own.
 

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Discussion Starter · #11 ·
I would invest in a refractometer. There is no way your salinity hasn't risen in two weeks with evaporation. I would also highly recommended purchasing an RO/DI unit and at least a handheld TDS meter.

Buying water is going to get very costly over the long run and you have no idea how pure the LFS water is. You're going to need salt anyway to maintain salinity so you're already going to be mixing your own.
I'll pick up a refractometer next time I'm there, but I'm running on a low budget at present so I can't stretch to a RO/DI unit yet, it is in my plans for the future though.

The salt in the tank won't evaporate, why would I need to add more to maintain it?
 

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You need to replace saltwater. When doing this you accomplish two things. When doing a water change you should be blowing off rocks with a powerhead or turkey baster to remove excess detritus. You should then siphon your sandbed to remove excess detritus. Siphoning the sand is how you get the water out of the tank. Then you would replace it with new salt water. By using new saltwater you are replenishing trace elements (calcium and the such) that living creatures consume.
 

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Discussion Starter · #14 ·
Yeah, I know the general maintenance routine, just given that I can't afford an RO unit at present, I don't see why I'd need to add salt to anything as I'll need to buy RO saltwater from the LFS for the time being anyway. I've got a spare powerhead for blasting the rocks and a siphon for cleaning the sand bed and water changes.
 

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Topping off water that has evaporated with Pure son saline water is something you need to do always to avoid fluctuations in salinity.
Removing some old tan water and replacing it with fresh salt mix is a water change and help dilute any waste byproducts of decomposition of waste in tank.
2 separate issues both important to tanks overall health
 

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Discussion Starter · #17 ·
So, I got a refractometer, and my water was exactly 1.025, but I'd still had some evaporate meaning I needed to top up. Topped the tank up with freshwater, as advised, and the SG is now 1.023. I assume I now need to add salt? Wouldn't it have been easier to top up with the saltwater I had ready? Seems my salt creep had coincidentally matched the evaporation meaning despite a lower water level I was still exactly where I wanted in terms of SG.
 

· Reef Junkie
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Depends on the refractometer, how long you let the sample equalize in temp and how soon after topping off that you tested. Did the top off match the the previous level?

Bet never add salt directly to an existing system with livestock.
 

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Discussion Starter · #19 ·
The refractometer is this one.

I left it for 20 minutes after adding the freshwater to circulate round and mix in, and let the temperature equalize for 1 minute (as that's what the instructions said to do). Yeah, I topped it back up to where it was before, I marked the tank when I originally filled it and had it at 1.025 so I'd know where to top up to.

There's no livestock in the system at present, just rock and sand whilst it cycles.
http://www.amazon.co.uk/RSG-100ATC-...&qid=1414691475&sr=8-1&keywords=refractometer
 
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