# Adding salt to a freshwater tank. **URL:** \ **Category:** Factual Questions\ **Created:** [April 7, 2010, 8:48pm UTC](https://boards.straightdope.com/t/adding-salt-to-a-freshwater-tank/535328 "2010-04-07T20:48:12Z")\ **Posts on this page:** 20\ **Page:** 1
**Author:** ![Belrix](https://avatars.discourse-cdn.com/v4/letter/b/ed655f/32.png) [@Belrix](https://boards.straightdope.com/u/Belrix)\ **Post date:** [April 7, 2010, 8:48pm UTC](https://boards.straightdope.com/t/adding-salt-to-a-freshwater-tank/535328/1 "2010-04-07T20:48:12Z")
I have a 50 gal freshwater tank. I add a little aquarium salt to the tank because it’s supposed to make the fish happier and healthier (and taste better 😉 ). As I clean the tank, I add more salt back with the new fresh water. If my measurements are accurate, The total amount of salt in the tank is basically stable. However, if I’m off a bit, the tank’s overall percentage might be skewing too far one way of the other. I’m worried about the latter. After a couple years of cleaning the tank, I don’t know if I’ve got the proper amount of salt in there. I bought a float-type hygrometer but testing it in water fresh from my tap and in the tank doesn’t show a measurable difference. I’m supposing that the device simply isn’t precise enough to do the job. What other options do I have to check the amount of saltiness in my tank? ---
**Author:** ![elfkin477](https://avatars.discourse-cdn.com/v4/letter/e/a9a28c/32.png) [@elfkin477](https://boards.straightdope.com/u/elfkin477)\ **Post date:** [April 7, 2010, 9:11pm UTC](https://boards.straightdope.com/t/adding-salt-to-a-freshwater-tank/535328/2 "2010-04-07T21:11:35Z")
You are probably right about the amount in your tank being stable if you always add the same amount as you change the water: the directions of the box of aquarium salt I have say to only add it after water changes because the salt does not filter out nor evaporate. ---
**Author:** ![Belrix](https://avatars.discourse-cdn.com/v4/letter/b/ed655f/32.png) [@Belrix](https://boards.straightdope.com/u/Belrix)\ **Post date:** [April 7, 2010, 10:13pm UTC](https://boards.straightdope.com/t/adding-salt-to-a-freshwater-tank/535328/3 "2010-04-07T22:13:03Z")
It’s only as stable as my ability to measure accurately, though. I’m not so sure about that part. ---
**Author:** ![Chief\_Pedant](https://avatars.discourse-cdn.com/v4/letter/c/a6a055/32.png) [@Chief\_Pedant](https://boards.straightdope.com/u/Chief_Pedant)\ **Post date:** [April 7, 2010, 10:30pm UTC](https://boards.straightdope.com/t/adding-salt-to-a-freshwater-tank/535328/4 "2010-04-07T22:30:18Z")
My african cichlids get a little salt whenever I feel like it. They seem to be healthy and I’m too lazy to measure. I do get salt deposits on the tank, so I’m guessing the water is pretty close to brackish by now… Anyway, just get a hydrometer (not a hygrometer) for measuring specific gravity that’s sensitive in the 1.0002-1.0010 range and have at it (if you want to be more scientific). One for saltwater tanks that only measures in a higher range won’t be sensitive enough. Various freshwater fish have various salinity tolerances. It does seem to keep diseases down but I don’t swap out my fish or add new ones very often. ---
**Author:** ![Chief\_Pedant](https://avatars.discourse-cdn.com/v4/letter/c/a6a055/32.png) [@Chief\_Pedant](https://boards.straightdope.com/u/Chief_Pedant)\ **Post date:** [April 7, 2010, 10:43pm UTC](https://boards.straightdope.com/t/adding-salt-to-a-freshwater-tank/535328/5 "2010-04-07T22:43:12Z")
[Possibly helpful link](http://www.wetwebmedia.com/ca/volume_4/V4I2/Brackish%20Systems/brackish.htm) _“In approximate terms, tropical aquarium seawater at SG 1.025 contains about 4.7 ounces of marine salt per US gallon (or about 35 grams per liter). So medium strength brackish water for a tropical aquarium at SG 1.010 will have about two-fifths that quantity of salt per gallon, or about 2 ounces of marine salt per US gallon. Low salinity brackish water at SG 1.010 will have even less salt, about 1 ounce of marine salt per US gallon. However, while measuring salt by weight is fine for estimating how much salt to buy and use, you will still need to measure the specific gravity of the water once you’ve mixed in the salt.”_ and \*\*\*Hydrometer or Refractometer? \*\* “While marine aquarists enjoy debating the relative merits of these two devices, for the brackish water aquarist the answer is very simple: use which ever one you like. A low cost floating glass hydrometer (costing around $5) is just as serviceable for the brackish water aquarium as a fancy refractometer (which will cost $40 or more). Brackish water fishes, by definition, don’t need precise salinities, and all your filter bacteria want is a steady salinity, the actual value doesn’t matter much. In other words, the error of margin resulting from the use of a even a cheap hydrometer will be well within the tolerances of the livestock being kept. This isn’t true for reef tanks where sensitive fish and invertebrates are being kept, hence the arguments of which specific gravity measuring device is best.”\* **NB:** I am not advising you on what salinity is best for your particular fish! NO REFUNDS on my marginally helpful advice! 😉 ---
**Author:** ![Ionizer](https://avatars.discourse-cdn.com/v4/letter/i/5daacb/32.png) [@Ionizer](https://boards.straightdope.com/u/Ionizer)\ **Post date:** [April 8, 2010, 12:26am UTC](https://boards.straightdope.com/t/adding-salt-to-a-freshwater-tank/535328/6 "2010-04-08T00:26:48Z")
Just my experience here. I ‘raised coral’ in a number of marine aquaria and have plenty of experience with adjusting salinity. If it helps to reassure you, it takes a LOT of ‘salt’ to raise salinity. A few tsps or such are basically next-to-nothing with ~50g tank (how much water is actually in there less the other volume-occupiers?). If you are only using a small amount to help buffer the water column, I would not worry about even measuring it much at all. You should be doing large enough water changes over period of time that should not allow saline to build up to high-ish levels anyways (right??)… I could always rely on the little plastic swingarm-in-a-box things that were usually about $10 or so. Remember that water temp can affect the readings, too, iirrc. ---
**Author:** ![Dinsdale](https://avatars.discourse-cdn.com/v4/letter/d/97f17d/32.png) [@Dinsdale](https://boards.straightdope.com/u/Dinsdale)\ **Post date:** [April 8, 2010, 1:15pm UTC](https://boards.straightdope.com/t/adding-salt-to-a-freshwater-tank/535328/7 "2010-04-08T13:15:26Z")
Just curious - what kinds of fish are you keeping? Because unless your fish prefer brackish water, I see no need to add salt. ---
**Author:** ![gravitycrash](https://avatars.discourse-cdn.com/v4/letter/g/977dab/32.png) [@gravitycrash](https://boards.straightdope.com/u/gravitycrash)\ **Post date:** [April 8, 2010, 3:02pm UTC](https://boards.straightdope.com/t/adding-salt-to-a-freshwater-tank/535328/8 "2010-04-08T15:02:49Z")
> [@Dinsdale](#): > > Just curious - what kinds of fish are you keeping? Because unless your fish prefer brackish water, I see no need to add salt. Exactly. If you have freshwater fish there is absolutely no need to add salt. I have two aquariums: 1 55g freshwater tropical and 1 46g freshwater tropical Cichlid tank. I’ve had the 55g for 8 years now and never have added salt and my fish buddies are all healthy and happy. Go to any reputable aquarium website with a message board and ask them about adding salt. Most of the answers will be like this: :dubious: I’m not trying to sound snarky so forgive me if I’m coming across that way. 🙂 ---
**Author:** ![TruCelt](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/trucelt/32/523_2.png) [@TruCelt](https://boards.straightdope.com/u/TruCelt)\ **Post date:** [April 8, 2010, 6:05pm UTC](https://boards.straightdope.com/t/adding-salt-to-a-freshwater-tank/535328/9 "2010-04-08T18:05:47Z")
If you add the same amount at each water change, then your salt level should slowly increase. This is because some of the water will evaporate, leaving a good amount of its’ dissolved salt in the tank. (Some of the salt also migrates onto the tank rim - I don’t understand how that part works.) The good news is it will increase slowly enough for your fish to adjust. The bad news is, depending upon the species, they will eventually top out and get sick/fragile. Guppies and Mollies, for instance, can adjust all the way up to brackish, but Discus will quickly succumb to small amounts of salt. ---
**Author:** ![Belrix](https://avatars.discourse-cdn.com/v4/letter/b/ed655f/32.png) [@Belrix](https://boards.straightdope.com/u/Belrix)\ **Post date:** [April 8, 2010, 8:21pm UTC](https://boards.straightdope.com/t/adding-salt-to-a-freshwater-tank/535328/10 "2010-04-08T20:21:13Z")
I’m trying to add the amount of salt appropriate to the water added. I don’t remember the ratio right now, it’s on the salt box, but if I add 10 gal of new water, and the ratio is 1 tablespoon per 5 gal, I add 2 Tbsp of salt for just the new water. Since the in-tank salt is only removed with the dirty water, I should have near-steady salt content. My worry is that I’m under-adding or over-adding by a bit each water change (since it’s difficult to measure water added, measure salt, etc) and I’m slowly drifting from healthy levels. ---
**Author:** ![TruCelt](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/trucelt/32/523_2.png) [@TruCelt](https://boards.straightdope.com/u/TruCelt)\ **Post date:** [April 8, 2010, 8:32pm UTC](https://boards.straightdope.com/t/adding-salt-to-a-freshwater-tank/535328/11 "2010-04-08T20:32:35Z")
No, because the remaining water int he tank will have a slightly higher salt/water ratio due to the water evaporating and leaving most of the salt behind. In order to maintain you would have to addback slightly less salt each time. As I said, this will happen very slowly, but you’ll end up with “Old Tank Syndrome” which is when dissolved solids have slowly increased over the years. You change ten gallons at a time - how often? I change 50% weekly, even in my 100gal which currently has a very low bioload. ---
**Author:** ![Belrix](https://avatars.discourse-cdn.com/v4/letter/b/ed655f/32.png) [@Belrix](https://boards.straightdope.com/u/Belrix)\ **Post date:** [April 8, 2010, 9:00pm UTC](https://boards.straightdope.com/t/adding-salt-to-a-freshwater-tank/535328/12 "2010-04-08T21:00:40Z")
I see your point. The way to avoid what you’re describing, old tank syndrome, would be to add fresh water to the full level before then removing 10 gal for changing. That would mean the water removed we have the same salinity as what is added. I try to change out 10 gal every other weekend. ---
**Author:** ![Dinsdale](https://avatars.discourse-cdn.com/v4/letter/d/97f17d/32.png) [@Dinsdale](https://boards.straightdope.com/u/Dinsdale)\ **Post date:** [April 9, 2010, 1:09pm UTC](https://boards.straightdope.com/t/adding-salt-to-a-freshwater-tank/535328/13 "2010-04-09T13:09:34Z")
> [@Belrix](#): > > I’m trying to add the amount of salt appropriate to the water added. I don’t remember the ratio right now, it’s on the salt box, … I’ve been called skeptical, but I believe the primary goal behind the labelling on many additives, is to get you to use as much of their product as they can get away with. You still haven’t told us why you are adding salt. Add a little pepper, and you’ll be on your way to a good bouillabaisse! 😃 Full disclosure, I suppose the fertilizers I add to my planted tank are in the chemical form of salts, but I think that is a somewhat different matter. ---
**Author:** ![Colophon](https://avatars.discourse-cdn.com/v4/letter/c/f05b48/32.png) [@Colophon](https://boards.straightdope.com/u/Colophon)\ **Post date:** [April 9, 2010, 2:01pm UTC](https://boards.straightdope.com/t/adding-salt-to-a-freshwater-tank/535328/14 "2010-04-09T14:01:35Z")
I thought this was going to be about a metaphysical puzzle… how much salt can you add to a freshwater tank? Cos of course, after the first grain goes in, it’s no longer freshwater… 😉 ---
**Author:** ![gravitycrash](https://avatars.discourse-cdn.com/v4/letter/g/977dab/32.png) [@gravitycrash](https://boards.straightdope.com/u/gravitycrash)\ **Post date:** [April 9, 2010, 2:32pm UTC](https://boards.straightdope.com/t/adding-salt-to-a-freshwater-tank/535328/15 "2010-04-09T14:32:26Z")
Seriously Belrix unless you have some sort of parasite problem there is no reason to be adding salt to your freshwater tank. To make matters worse, depending on the salt concentration, you could be harming the beneficial bacteria colony in your tank. I just looked at a website for aquarium salt. They state that adding aquarium salt is somewhat controversial, um yeah. Just saying man. 🙂 ---
**Author:** ![Belrix](https://avatars.discourse-cdn.com/v4/letter/b/ed655f/32.png) [@Belrix](https://boards.straightdope.com/u/Belrix)\ **Post date:** [April 9, 2010, 4:03pm UTC](https://boards.straightdope.com/t/adding-salt-to-a-freshwater-tank/535328/16 "2010-04-09T16:03:31Z")
It’s supposed to thicken the fish’s slime coat & keep it healthier is all I know. For a long time I just used water and only water but the fish store suggested this. The biggest problem I’ve ever had in two years with this tank (the first year or more was without salt) is a tendency to grow algae (I should change the water more often) and a rather voracious catfish that was decimating the population until I adopted him out. (Amazing how big their mouths can open.) You’re suggesting I just not do salt at all, then… ---
**Author:** ![gravitycrash](https://avatars.discourse-cdn.com/v4/letter/g/977dab/32.png) [@gravitycrash](https://boards.straightdope.com/u/gravitycrash)\ **Post date:** [April 9, 2010, 7:38pm UTC](https://boards.straightdope.com/t/adding-salt-to-a-freshwater-tank/535328/17 "2010-04-09T19:38:41Z")
Yes, I would remove all of the salt from their environment but since they are used to living with some salt you don’t want to remove it all at once or you will stress them. The goal for an aquarium, besides keeping your fish healthy, is to try and mimic their natural environment as much as possible and for the most part salt isn’t in it. I’m just curious about what kind of catfish you had because Corydoras (the most common for aquariums) are piscivorous and peaceful fish. ---
**Author:** ![Dinsdale](https://avatars.discourse-cdn.com/v4/letter/d/97f17d/32.png) [@Dinsdale](https://boards.straightdope.com/u/Dinsdale)\ **Post date:** [April 9, 2010, 7:50pm UTC](https://boards.straightdope.com/t/adding-salt-to-a-freshwater-tank/535328/18 "2010-04-09T19:50:32Z")
> [@gravitycrash](#): > > I’m just curious about what kind of catfish you had because Corydoras (the most common for aquariums) are piscivorous and peaceful fish. Next time you are in a PetSmart or something, check out the cats they label as peaceful, community fish. All kinds of pictus and - my fave - “bullseye” cats (H. Brachysoma). Nocturnal ambush predators that will eat anything they can fit in their mouths. My sister once gave me a small bullseye - the last survivor of a 10gal her kid lost interest in. Tossed it into my heavily planted 55, and lost all of my “dither” fish (danios and tetras) as the sonofagun grew to 10" before kicking. I saw them in a big box pet store advertised as peaceful and maxing out at 3"! 😛 ---
**Author:** ![Belrix](https://avatars.discourse-cdn.com/v4/letter/b/ed655f/32.png) [@Belrix](https://boards.straightdope.com/u/Belrix)\ **Post date:** [April 9, 2010, 8:23pm UTC](https://boards.straightdope.com/t/adding-salt-to-a-freshwater-tank/535328/19 "2010-04-09T20:23:32Z")
I don’t know what kind of catfish he was, he was a transplant from my Brother in Law’s abandoned tank. Silver & gray with mottled spots on his back and long whiskers (the cat liked to watch him through the glass). He also had spines on his fin tips (which got tangled in the net during a transfer attempt). He was about 7" long when I adopted him out. He picking off about 2 or 3 fish a week at his most hungry. Yup - disappeared overnight - even the fast ones were susceptible. ---
**Author:** ![Dinsdale](https://avatars.discourse-cdn.com/v4/letter/d/97f17d/32.png) [@Dinsdale](https://boards.straightdope.com/u/Dinsdale)\ **Post date:** [April 9, 2010, 8:41pm UTC](https://boards.straightdope.com/t/adding-salt-to-a-freshwater-tank/535328/20 "2010-04-09T20:41:58Z")
Sounds like a [pictus](http://aqualandpetsplus.com/Catfish,%20Pictus.htm). Readily available at just about every LFS. Really cool fish, but definitely not for the community tank with smaller fish.