What salinity for a fish only tank

[Miami Reef]

What salinity should be kept for a fish only tank?

Solely for the benefit of fish health. Do they do better in the high range (1.026) or lower range (1.022).

It’s also important to me that nitrifying and other bacteria establish themselves quickly to handle waste, so what salinity is all around good for a fish only tank?

Do not recommend a salinity solely for the purpose of saving money. I want to keep a salinity that will keep my system and fish healthy.

@Randy Holmes-Farley

 

[mdb_talon]

I dont know an exact ideal number but i have always heard many places keep fish only systems between 1.020 and 1.023 not only for cost but also reduced chances of parasites...i dont actually know if this is accurate though.

I am sure @Jay Hemdal would be able to give insight.

 

[Jay Hemdal Verified Community Expert]

I dont know an exact ideal number but i have always heard many places keep fish only systems between 1.020 and 1.023 not only for cost but also reduced chances of parasites...i dont actually know if this is accurate though.

I am sure @Jay Hemdal would be able to give insight.

Deja vu all over again (grin). I just posted my opinion a week or so ago:

There is no best single value, it is rather, a range and that range can be different for different species.

The first thing to do is ensure you have an accurate means to measure salinity. Then, understand that there is some confusion between salinity and specific gravity, as the latter has a temperature component to it that needs to be accounted for.

That all said, for most coral reef fishes, I prefer a specific gravity of around 1.021, or a salinity of around 28 ppt. This saves a bit on salt costs, and allows for slightly reduced osmotic stress in the fish. However, many people set up "fish only" tanks and then add snails and other invertebrates, this changes the definition then (grin). Sharks and rays do better in full strength seawater.

Jay

 

[Miami Reef]

Thanks. I have another question:

Am I allowed to strip my phosphates to 0.00000? Or do fish absorb needed phosphates from the water?

 

[Supa]

Deja vu all over again (grin). I just posted my opinion a week or so ago:

There is no best single value, it is rather, a range and that range can be different for different species.

The first thing to do is ensure you have an accurate means to measure salinity. Then, understand that there is some confusion between salinity and specific gravity, as the latter has a temperature component to it that needs to be accounted for.

That all said, for most coral reef fishes, I prefer a specific gravity of around 1.021, or a salinity of around 28 ppt. This saves a bit on salt costs, and allows for slightly reduced osmotic stress in the fish. However, many people set up "fish only" tanks and then add snails and other invertebrates, this changes the definition then (grin). Sharks and rays do better in full strength seawater.

Jay

I would say 1.024 would be ideal that way you could drop a softie in later if you decide to spice it up some. As mentioned above lots of fish stores keep the fish in lower salinity then you bring them to your house and higher salinity and the fish problems become visible.

 

[AquaBiomics]

That all said, for most coral reef fishes, I prefer a specific gravity of around 1.021, or a salinity of around 28 ppt. This saves a bit on salt costs, and allows for slightly reduced osmotic stress in the fish.

Why do you consider normal (35 ppt) salinity, the salinity these fish evolved in, to be osmotically stressful?

My understanding is that marine fish are well suited for dealing with this level of salt, drinking constantly to replace osmotic water loss and dumping excess salt via the gills and urine.

In fact, normal seawater is osmotically closer to fish internal fluids than freshwater. Freshwater is the more osmotically stressful environment in absolute terms.

But you're no novice :) Your statement must be based on some evidence, so I'm curious to hear the reasoning. Thanks.

 

[Big Smelly fish]

Back in the 70’s before reefs tanks came popular, most places recommended 1.019 to 1.021 and everything did fine. I haven’t read the early books is a long time, but think that’s what was recommended back then.

 

[wonroc]

I spoke to my local fish store, which is one of the biggest in NJ. They tell me they keep their salt fish only tanks at around 1.7, 1.8. Less stress

 

[Malcontent]

Salinity of blood is something like 9 ppt which is less than seawater but more than freshwater. When freshwater fish are stressed for whatever reason, adding salt to the water can reduce the rather large energy demands of osmoregulation in a FW environment.

For saltwater fish, lowering the salinity should have a similar effect.

Both types of fish may be well adapted for their environments but it doesn't mean those environments are optimal for them.

 

[Jay Hemdal Verified Community Expert]

Why do you consider normal (35 ppt) salinity, the salinity these fish evolved in, to be osmotically stressful?

My understanding is that marine fish are well suited for dealing with this level of salt, drinking constantly to replace osmotic water loss and dumping excess salt via the gills and urine.

In fact, normal seawater is osmotically closer to fish internal fluids than freshwater. Freshwater is the more osmotically stressful environment in absolute terms.

But you're no novice :) Your statement must be based on some evidence, so I'm curious to hear the reasoning. Thanks.

Certainly marine fish have evolved to live in seawater, but fish's blood is hypotonic to seawater. The general understanding is that keeping them at slightly lower salinity reduces the effort their bodies need to expend to maintain homeostasis. This is not universal though. One would think then, that freshwater fish, having blood hypertonic to their water, would benefit from the addition of some salt. For many species of freshwater fish, that is true - but it is not true for some soft, acid water fishes. For marine fish, we know that sharks and rays do best in full strength seawater. It has been opined that Red Sea fish should be kept at normal salinity (which is lower than normal for them).

Jay

 

[Jay Hemdal Verified Community Expert]

Thanks. I have another question:

Am I allowed to strip my phosphates to 0.00000? Or do fish absorb needed phosphates from the water?

Interesting question - I think you have too many zeros there, but let's say you drop P to 0.01 mg/l. Marine fish drink water, but I wasn't sure if uptake of calcium and phosphorus was across the gills or through dietary intake. I presumed the latter, but I didn't know. I found this snippet of text:

Food is the main source of P for fish because FW and SW are low in phosphate. Thus, regulation of phosphate is considered more critical than that of Ca because fish must effectively absorb and conserve phosphate in both FW and SW environments. Dietary P concentration is a major regulator of P metabolism in fish.

In this article: https://www.ncbi.nlm.nih.gov/pmc/articles/PMC8466162/


Jay