You're almost certainly going to have one. It happens. Too much fresh water goes in. Topoff screws up. Or shuts down and you come back from your trip to find the system water level is way down. Whoa! way down!
First thing, don't panic. This is a two-direction problem. If you got overdosed with fresh water, that LOWERs your salinity and you probably have too high a water level going on. If you got underdosed with fresh water, that RAISES your salinity because of evaporation, and your water level is probably low.
The second situation, high salinity, is fairly benign and you can correct it fairly easily: just add ro/di, not necessarily all at once, but just about 1/10th of the deficit every 15 minutes until you reach normal. Fish and even corals are fairly tolerant of a LOWERING of salinity over a short-ish time, which is what you're doing by ADDING more fresh water. Yep, I know that's messing with your head, lowering it by adding....but think of it as using fresh water to restore normal balance.
The dangerous FIRST situation, too low a salinity, (and usually too much water in your system) is the one you need to slow way down for. You've got too little salt in the water, or you've got too much fresh water, however you want to think of it. Fish do not tolerate a rapid RISE in salinity. In this case, if things are alive, things aren't the worst, and nothing's going to change in the next few hours, or even the next day, granted this did not happen 15 minutes ago. What you need is less fresh water---relative to the salt. How to do that? LET IT EVAPORATE. If it's not below 1.020, just let the water evaporate without topping off, and the salt level will rise at a safe rate over the next couple of days, nothing damaged. If you ARE below 1.020, make some salt water (takes 24 hours with a mixing pump, to get ALL the elements dissolved: salt water isn't ready until it's clear. Clear. Crystal clear.--------Then start topping off with salt water. Likely your water is too high. So dip out a cup or so of tank water and replace it with 1.024 water. Using your refractometer, and ( important!) allowing time for total mixing of water in tank---you should raise salinity no more than .002 per 15 minutes. Fish don't like salinity to RISE fast. Once you have a good salt reading, at the proper water level, you can resume normal fresh water topoff.
Situations like this are why you need a refractometer. They aren't that pricey, and sure beat having to whack a swing-arm hydrometer on the table 20 x to get the bubbles off the swing-arm---which ruin the reading.
First thing, don't panic. This is a two-direction problem. If you got overdosed with fresh water, that LOWERs your salinity and you probably have too high a water level going on. If you got underdosed with fresh water, that RAISES your salinity because of evaporation, and your water level is probably low.
The second situation, high salinity, is fairly benign and you can correct it fairly easily: just add ro/di, not necessarily all at once, but just about 1/10th of the deficit every 15 minutes until you reach normal. Fish and even corals are fairly tolerant of a LOWERING of salinity over a short-ish time, which is what you're doing by ADDING more fresh water. Yep, I know that's messing with your head, lowering it by adding....but think of it as using fresh water to restore normal balance.
The dangerous FIRST situation, too low a salinity, (and usually too much water in your system) is the one you need to slow way down for. You've got too little salt in the water, or you've got too much fresh water, however you want to think of it. Fish do not tolerate a rapid RISE in salinity. In this case, if things are alive, things aren't the worst, and nothing's going to change in the next few hours, or even the next day, granted this did not happen 15 minutes ago. What you need is less fresh water---relative to the salt. How to do that? LET IT EVAPORATE. If it's not below 1.020, just let the water evaporate without topping off, and the salt level will rise at a safe rate over the next couple of days, nothing damaged. If you ARE below 1.020, make some salt water (takes 24 hours with a mixing pump, to get ALL the elements dissolved: salt water isn't ready until it's clear. Clear. Crystal clear.--------Then start topping off with salt water. Likely your water is too high. So dip out a cup or so of tank water and replace it with 1.024 water. Using your refractometer, and ( important!) allowing time for total mixing of water in tank---you should raise salinity no more than .002 per 15 minutes. Fish don't like salinity to RISE fast. Once you have a good salt reading, at the proper water level, you can resume normal fresh water topoff.
Situations like this are why you need a refractometer. They aren't that pricey, and sure beat having to whack a swing-arm hydrometer on the table 20 x to get the bubbles off the swing-arm---which ruin the reading.
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