Fish Acclimation to Lower Specific Gravity QT

[Rython]

I generally try to simply have my QT water match the Specific Gravity of the incoming fish's bag water so I only have to temperature match and I don't have to risk ammonia build-up with a prolonged drip style acclimation. However, there have been circumstances where that wasn't possible. For example, i'm going to QT two fish together, one from Live Aquaria at SG of 1.018 and one from Diver's Den at 1.025.

In the past, I've read an upward move in SG of .001 will not bother fish, and neither will a much greater downward move. Some have argued that as long as you are moving to lower SG any difference is fine.

Last time this happened I set the QT SG at 1.025 and drip acclimated the fish that came in a 1.018. I'm wondering though if I could have simply set the QT at 1.018 and moved both fish right in after temperature acclimation.

What are your experiences with transferring fish to lower specific gravity water?

 

[Brew12]

I'm selecting "Depends on the fish".

Some species of fish are more sensitive to salinity swings than others. Within a species not all fish will react the same to a change in salinity. An extreme case of this is the Molly. Normally a fresh water fish, they can acclimate to salt water. Some people take them from fresh water and put them into their salt water tanks with great success. Others have tried and have lost the fish and will tell you that drip acclimation is mandatory.

My opinion is that this is like so many other things in the hobby. You can possibly get away with a 0.005 swing up or down, maybe larger. Just like you can get away with alkalinity swinging up and down by 2dkh some times. The healthier the tank or the fish, the less likely it is to be harmed by a single factor. If you get a fish in that has gill damage or had an extremely stressful and delayed experience since capture I feel it is less likely to survive a salinity swing. If it is a healthy fish that was captive bred and raised that you pick up from the breeder? It could likely handle a significant salinity swing.

That is the best non answer I could come up with.

 

[Rython]

So I take it you don't buy into the idea that it's easier to go down in salinity than up? It's just the difference that matters?

 

[chipmunkofdoom2]

From a theoretical standpoint it might be easier to go down than up, but either way, it's a pretty extreme change. You're either driving salinity down by 31% or driving it up by 42%. I wouldn't do either.

I wouldn't ever intentionally put myself in a situation where I had to make this choice. But if the situation came up, I'd set up one of the fish in the QT and set the other fish up in a 5g bucket (or an appropriately sized glass tank/Rubbermaid tote). I'd make the salinity in the bucket match the one fish and the salinity in the QT match the other. I'd have basic life support in the bucket, like a heater, air stone and seeded biological media. I'd then make the salinity in the bucket match the QT tank over the course of a day or two. Then both fish can be QTed at the same salinity.

 

[Brew12]

So I take it you don't buy into the idea that it's easier to go down in salinity than up? It's just the difference that matters?

Sorry, I didn't mean to imply that but I think I did.

Going up is harder on the fish. How much harder is subject to debate but osmotic shock is worse when raising salinity. From studies I have read, a fish may live for 2 to 4 days after a fatally rapid increase in salinity. Because their is such a delayed reaction I feel it is hard to quantify actual fish losses due to improper acclimation. Hobbyists have no way to analyze the actual cause of death at that point.

 

[Rython]

From studies I have read, a fish may live for 2 to 4 days after a fatally rapid increase in salinity. Because their is such a delayed reaction I feel it is hard to quantify actual fish losses due to improper acclimation. Hobbyists have no way to analyze the actual cause of death at that point.

That is really useful to know. I always assumed they would go downhill fast from an osmotic shock event and you'd know pretty quickly that you screwed up. Makes me wonder if any of the fish i've lost on days 2-4 with no outward signs of disease were really killed by my flippant disregard of what I perceived to be small salinity differences. I've moved fish up 0.001 without worrying about it but i've also moved them down 0.003 assuming the lower pressure would be easier on them if anything.