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Old 08-01-2009, 08:57 PM   #11
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Originally Posted by Tank2379 View Post
Ok... So what your saying is I can't top off my Water with saltwater that's already prepared @ 1.026 since my water parameters are already @ 1.026?
This is where it's gone wrong. If some water has evaporated from your tank that started at 1.026, what remains in the tank is now higher than that. Maybe not enough to show up on the hydrometer yet, depending how much water we're talking about replacing, but over time it will go up without limit if you add salt every time.

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Old 08-01-2009, 09:00 PM   #12
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Originally Posted by Tank2379 View Post
LOL... I understand the concept of water chemistry and quality just trying to start a debate.... but anyhow if I do weekly water changes and topping off during the week with RO water. How do I know if my Salinity will not raise with weekly water changes compared to topping off and my salinity staying at a steady 1.026? I mean I am using a Refactometer.
If you say take 50 gallons of water at 1.026 salinity out of a 100 gallon tank you add back 50 gallons at 1.026 that way in theory the salinity should be exactly the same. Does that help?

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Old 08-01-2009, 09:15 PM   #13
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If you have a line for your water level and you top up with RO every day to that line; even if you don't test (I would not recommend) your SG should remain the same. If you top up to the line and then do your 'general maintenance' water change with sea water or pre mixed saltwater (I use sea water) your SG should be constant.

This very simplistic but you get my point.
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Old 08-02-2009, 02:19 PM   #14
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Also on a PWC you are taking salt out and then adding salt back in. On evaporation and top offs salt stays in and salt is added.
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Old 08-02-2009, 03:13 PM   #15
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Maybe think of it as a ratio. Since that is essentially what sg is. It’s a ratio of what a given volume of your water weighs compared to what the same volume of pure water weighs. Since we know that water and not salt evaporates, over time the ratio between water and salt will change. The ratio of salt to water in a given volume will now be a little higher. We correct that by adding pure water back to reset that ratio back to where we want it to be. If we used water that has salt added to the tank, we just added a little pure water plus some more salt. Depending on how long you wait between topping off, you may not see the change in the sg of the system the first time. Over time and repeated topping off with salt water you will see the sg of the system raise.

Water changes are just that. You are changing out some of the existing water with water of similar properties. Just like was mentioned earlier, this helps dilute some of the buildup of unwanted compounds as well as replacing trace elements that are needed.
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Old 08-03-2009, 10:33 AM   #16
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Along the lines of what Razorbacksfan said...

Think of it this way. If you have a 10g tank at 1.026 and let 5g of it evaporate away, the water in the tank is NOT still 1.026 - it is quite a bit more. Now if you dump 5g of RO/DI water in the tank, you'll be back at 1.026. But if you dump 5g of saltwater at 1.026 into the tank, then you'll end up somewhere below where you were with 5g, but above 1.026.

If you're only replacing a little bit of evaporation each day, you won't see the rise in salinity even with a refractometer. But if you constantly replenish that evaporation with saltwater over the course of a week, you WILL see a rise in salinity.

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