Some questions about going brackish.

[Aiya Quackform]

I'm planning on getting a F8P soon, and I'm still a bit confused on the whole converting to brackish thing.

I'll be doing weekly 15-20% water changes for a 10g with UGF, one F8 only.

Should I up the salt every week, or every other week?
Also, I'm confused as to how I go about uping the salt. Every week, do I make one gallon to be replaced have a salinity of 1.006? (I know that's not a salinity measure, it's specific gravity or something, but you know what I mean.) That, in theory, would increase the water's salinity to 10% of the desired final outcome--1.006. Or, should I go slower? WHAT DO I DO?!

Oh, the desired "specific gravity" of F8-friendly brackish water is 1.005-1.008, right? Also, I need marine salt, not aquarium or regular salt, correct?

[RTR]

The conservative approach is no mare than a 0.002 specific gravity change per week ( and yes, it is with marine mix, not aquarium salt). This not a fire, there is no big rush. That same level of change every two weeks is even safer.

But your partial water changes may need to a bit larger in volume. Monitor the nitrate titer for best guidance on this. You want to minimize the nitrate levels in the tank at the lowest figure you can manage. These are long-lived fish, but to make that lifespan they do need to have very clean (low nitrate, low organics, water - you cannot measure most pollutants in the water, but you can easily monitor nitrate).

HTH

[Aiya Quackform]

I should note that the tank will be cycled before the puffer is put in.

*does some quick math* Alright, how does this sound, assuming that the first week's water change is 7 days after putting the fish in.

1st Week: 2 gallon water change, fresh water (not freshwater) has an SG of .010, which when dilluted in a 10g tank, will have the affect of uping the tank's SG to .002.

2nd Week: Replace 2 gallons with fresh water at an SG of .002.

3rd Week: 2 gallon water change with SG of .010, resulting in SG of .004.

4th Week: 2 gallon replacement with SG of .004.

5th Week: 2 gallon water change with SG of .010, resulting in tank-wide SG of .006.

Regular water changes after this point have an SG of .006 per gallon.

How's my math?

[Bred]

Your process seems good, but keep in mind that a 10g tank does not actually hold anywhere near 10 gallons. Add gravel and decorations and it holds considerably less.

If you want to know actual water volume, completely empty (or completely fill) using a measuring container. Standard rubbermaid utility buckets often have internal gradations showing volume in gallons (or litres).

//...Actually I think your math might be a bit off, too. *thinks hard*

Yeah, got it. Your math doesn't take into account the salt removed with the 2g water change. For example, when your tank SG is at 0.004, replacing 2g with 0.010 will only raise the salinity of the whole tank by 0.0012

2 gallons of the tank was 0.004, is now 0.010
net difference in salinity is .006 per gallon of water changed
the effect of this raise on the entire tank is (0.006/10) = 0.0006 per gallon of water changed
which we double, since you changed 2 gallons - 2x0.0006 = 0.0012

Make sense? I've edited this post 19 times now trying to clarify it further... Hope that helps.

[Aiya Quackform]

*takes long, hard look at Bred's post*

Okay, I think I've got it. So the replacement water needs to have an SG of .010 + the SG of the tank? So, if the tank is currently at .004, the 2 gallons of replacement water must have an SG of .014?

[Bred]

Yup, that's right!

Now, keep in mind that if you make the transition slower & smoother, you and your beneficial bacteria will sleep better at night - as RTR points out above. Making a (relatively) instantaneous 0.002 increase in SG is borderline sketchy.

Also, knowing the real volume of your tank will help a lot right now and down the road if you ever need to change the salinity or (knock on wood) medicate the tank. You should measure it now while you can.

[RTR]

LOL @ Bred & AQ - the math for BW partials is far worse than the changes themselves.

But I do agree that "nominal volume" and "working volume" are two unrelated concepts. There is effectively no way to set a general rule for reconciling those two ideas. Being a scientist, I want to know so I do measure (by the terribly imprecise scaling on the Rubbermaid buckets already mentioned) the actual total contained volume when I first do any setup. That is far better than not knowing for me. That is also the only time in any given setup's life I still carry buckets.

It is also not a requirement that the increase in specific gravity be precise - this is not medication delivery. If it is below projected densities, that is conservative and safe. You would only have concerns if your increases were well above the projected densities, and the greatest danger there is the risk to the filter bacteria. You can drop-acclimate a BW fish in hours. You are on thin ice if you do that with your bacterial colony - they are far more sensitive to that particular change than are the fish (which are adaptable to water density changes already by their nature).