Do I need to adjust my Specific Gravity?
 

Hi all, newbie here. :biggrin:

I just bought/moved an existing FOWLR tank last weekend. The previous owner apparently kept the SG at 1.024. We moved 100+ gallons of exisiting water (it's 135g with sump), and the new water was also tested at the time we added it (I'm not exactly sure what it was, the prev. owner checked it). So I'm quite baffled as to why now, not even a week later, the SG could drop to 1.019. I did change out about 15 gallons a couple of days ago (the nirtrate was climbing), and the SG of that change water was about 1.019, but I figured that 15 gallon wouldn't drop the overall SG. It doesn't make sense it could have dropped, so I'm a little suspicious of the hydrometer.

But if my SG really IS 1.019 (the readings are consistant), is it harmful to the fish or rocks to be at this level? Most fish seem fine, a couple seem lethargic but I don't know what they are normally like. What advantage would there be in bringing it up? How do I bring it up? I mean, I know you add salt, but how on earth do you gauge how much? From what I've read bringing it up too fast could be problematic.

Thanks for your help!

check your hydrometer, they do go bad and this article on bogus info

Sg
 

I would bring it up to 1.022.

1.022 to 1.026 is normal for FO and FOWLR tanks albeit there is no good reason to have it any lower than 1.025, where reefs should be 1.025 to 1.026. :)

Best bet it to either buy a refractometer $50-60 and periodically recalibrate your hydrometer (I've seen them off by as much as 0.008), or take a water sample to your LFS and get them to test with a refractometer so you can figure out how much yours is off by. I have two hydrometers (one is SeaTest and one is Coralife...I think); one is under by 0.002 and the other is over by 0.002.

For a really rough guestimate...about 2 tbsps will raise the sg by about 0.006 or 7 ish in 5 gallons. This is just my guestimate from mixing salt up in my buckets.

Unless I'm reading this wrong, I would think you'd need 5x that much (10 tbsps) to raise 5g by 0.006. According to Instant Ocean directions 2 1/2 cups will raise 5g to ~ 1.024.
1.024 - 1.000 = 0.024
0.024/4 = 0.006
2 1/2 cups = 40 tbsps
40/4 = 10
Therefore, would it not take 10 tbsps of salt to raise 5g of FW (1.000) to an SG of 1.006?

Thank you for you replies. We use refractometers where I work, and check the zero (I think what you call calibrating) daily, as well as run two known controls. So I know they are accurate. I will take a sample in and check it.

So, if the SG is low, how might this affect the fish? The Stars and Stripes puffer seems very lethargic, and he was actually puffed this morning when I went down there. The dog might have scared him. He ate some food off a stick the second day or so, but I haven't seen him eat since. I also haven't seen the lion fish eat since the second day or so. Everyone else (2 triggers, another puffer and a wolf eel) are eating like pigs. I tested the water yesterday, and it was neg for ammonia, nitrate and nitrite, and the pH was 7.8 (which is what it has been since I got the tank). Is that a little low?

Thanks again.

Well I did say it was a really rough guestimate, but it takes about 3 1/4 cups to get the sg to 1.026. I know that for sure because I put 3 cups and a bit in, and then I add a little more to adjust it.

Higher oxygen saturation in the water and ionic regulation of salt from the fish should be easier at a lower salinity. Nothing wrong with 1.019, I know a few FOWLR tanks running for many years at 1.018.

As for the Stars and Stripes, it shouldn't be the salinity bothering him. They often spend their juvenile lives in Brackish water estuaries. He might just be a lazy puffer as so many are.

As much as I'm aware of this I've personally seen no benefit, and I don't see any rationale to keeping the salinity so far away from NSW.

So, I tested with the refractometer, and the reading was 1.016. So the hydrometer is inaccurate, but not in the direction I had hoped! I did add some salt today and will add more. I did'n't want to bring it up too fast.

That's pretty low. Aim to raise it about 0.001 per day.

That's what I did today... brought it up .001. I think I put in over 5 cups of salt!

It will take quite a bit...can't remember how big your tank is without going back to page 1 though, and I'm too lazy (tired) to do that right now. :lol: You aren't pouring the undissolved salt right into the tank are you? The best way to do it is to siphon out some tank water, add salt to that, and pour it back in. Or, do a 10-25% waterchange and mix the new sw to a higher sg.

It is 135 gallon tank with a 40 gallon sump. Midweek I changed out 15 gallons (nitrate was a bit high), and tonight I changed out 10 (slight ammonia). I mixed the extra salt in to the water going in, and then put it into the sump (and also via bucket right into the tank). Tomorrow I think I'll just add as much water as it takes to dissolve several cups of salt. I figure the higher the SG, the less salt it takes to bring it up 0.001. Do you agree?

Yes, but not by very much...although I'm having difficulties wrapping my brain around that right now. :lol:

Ah, that's why it took so much salt. That's a lot of water volume. After the initial cycle, your tank should never have ammonia or nitrite. The presence of either is called a mini cycle, and means that you have done something to either damage the biofilter or you have added new critters which are demanding a bigger biofilter and it will take a bit of time for the biofilter to catch up.

I have to disagree with this, as it is one of my pet peeves. Ammonia and nitrite are always present. It is undetectable test readings which are desired, indicating extremely low levels of both.