Confused - ph, kh, gh, salinity - what's most important?

[ukgoffer]

I have a brackish tank that I want to raise to "medium" salinity levels. Right now it reads 1.008 via hydrometer and refractometer. My PH is 7.8. Ammonia and nitrates are nil. My LFS checked the salinity via refractometer for me - while it was ok, they said my GH was too high (over 22). I'm a bit stumped on what's most important. The shop suggested I do a 50% wc and not add any salt. Can anyone add any clarity for me?
1 7" dat
2 silver scat (6" and 7")
2 2.5" red scat
2 8" Columbian Shark Catfish
2 3" Monodactylus
1 rogue firemouth
1 large blue Malawi crab

 

[Pomatomus]

Well it sounds like your water source is hard then. Here's a quick tutorial:

pH is the concentration of protons (hydrogen ions, H+) in the water. The more protons there are, the more acidic the water is (low pH). The fewer there are, the more basic it is (high pH). a pH of 7 is neutral. Pure water has approximately a pH of 7. As waste is produced and decays in the aquarium it will slowly acidify the water over time.

KH is known as alkalinity, or "carbonate hardness". It is not the same as hardness. It's a measurement of carbonate (CO3-) ions in the water. Carbonate ions are pH buffers, meaning that they cause the water to resist changes in pH. In the presence of excess hydrogen ions (positive), carbonate ions (negative) will react, creating carbon dioxide and water. So as waste accumulates in your aquarium and more protons are produced, carbonate will be consumed. This is why people often add "buffers" to raise their pH. Most buffers (such as baking soda, aka sodium bicarbonate) are carbonate-based and replenish the alkalinity of the system.

Note: Freshwater environments vary a lot in alkalinity. Amazonian fish are used to very low alkalinities, whereas rift lake cichlids are used to more alkaline water. Areas with lots of minerals such as limestone (calcium carbonate) have higher alkalinities than those without. Marine environments have high alkalinities as well, and thus their pH's are usually higher (around 8). This is because shells and coral skeletons are also made from calcium carbonate, which buffer the water in addition to other sources. That's why in saltwater tanks you usually add "crushed coral / aragonite / calcium carbonate" sand or gravel, and live rock or base rock. These all help stabilize your system's pH and KH.

GH is known as "hardness" or "general hardness". It refers to positively charged ions in the water, specifically minerals with a 2+ oxidation state (so not hydrogen, which is 1+). A couple of examples would be calcium, magnesium, strontium, etc... I have to be honest, it's quite rare to hear of a GH being too high for marine tanks, but I don't know what the target would be for brackish tanks. Also, it's very rare for a store to actually test for it because it's usually much less significant than pH and KH for most fish, excluding things like discus and rift lake cichlids.

Now to really get into it: What was your calcium at? A high level of calcium can influence your GH, and calcium can build up as your tank gets dirty. Calcium carbonate will dissolve in water so slowly (up to a certain concentration, which is safe) that you can't notice it, but it does. This puts calcium ions (Ca2+) and carbonate ions (2xCO3-) into the water. Hydrogen ions (H+) will react with the carbonate in the reaction described above. Since there are fewer carbonate ions in the water, more calcium carbonate will dissolve from your live rock or live sand. So the carbonate is exiting the system, but the calcium is steadily building up! Water changes and lower bioloads can fix this issue.

But what I would recommend that you do is a couple of water changes with your normal amount of salt, but mix it into reverse osmosis or distilled water instead of tap water. Tap water contains all sorts of minerals depending on your location and it's very likely causing your hardness issues. Distilled and reverse osmosis water shouldn't have any ions so all that you're adding are the ones from your salt.

I hope this helps. Sorry it's a little tl;dr

 

[ukgoffer]

This is great info and much more clear to me. Thanks. My tap water does not test hard - about 4 or 5 - but I will still do the next few wc with distilled water. I am running both 2213 and 2217 Eheim canisters so the filtration should be more than sufficient. The substrate is 80% clay based and 20% sand. This was once a planted tank but I converted it to brackish after my 125 sprang a leak. I am guessing the tank mates on top of massive amounts of dying java ferns (the scats are tough on anything green - tearing up more than they eat), brown algae and heavy feeding has pushed the bioload to excess. I've cut the light to 6.5 hours, reduced frozen foods but increased live minnows (I timed the last feed - 16 minnows in 6 minutes) to 2x per week from 1x. I'm also going to pull what's left of the java fern until I get the balance right. Would you stay away from API Water Softener Pillow? Is it only for freshwater?

 

[Pomatomus]

I've never used that product, but I wouldn't use something like that in a saline environment. A lot of those things will affect the constituents of the salt you're using.

I really wouldn't worry about it too much. If you trust that your LFS knows what it's doing then don't let me stand in the way, but I don't see how you can have a saline environment without calcium and magnesium. I would still follow my recommendation, because that would theoretically reduce your dGH from 22ish to 17ish with a 100% change. The ions present in your salt are just being added to those in your tap water.

But having worked in 2 fish stores and for an aquarium maintenance company I feel that these guys may not know what they're doing. Like I said, it's rare to check GH unless it's for very specific freshwater environments. Also, by using the conversion factor of 17.8, you can figure out your GH in ppm as opposed to dGH. 22 x 17.8 = 391.6

...and according to these sites, you are probably still in the safe/typical range:

http://www.versaquatics.com/testingthewater.htm

This site quotes a bit low for all marine parameters IMO. For example, I would NEVER keep a reef tank below 8dKH. So although it says 20dGH is the maximum, I think it's probably higher. Either way you're close.

http://www.liveaquaria.com/general/general.cfm?general_pagesid=352

 

[ukgoffer]

The API product was just something I saw on the web. My LFS is actually an aquarium maintenance company, primarily marine. I get dueling advice depending on who I talk to. IMO I think the issue is that Bob is treating my fish like ciclids which they really aren't. Bar the rogue firemouth I've got a true brackish crew. I'll stick with your advice - I've got 20g of distilled water, just trying to dissolve the salt. Thanks

 

[ukgoffer]

I just did a 25% wc with distilled water and my gh is still off the charts (at 100 drops with the API kit, the water was red - still not green). My tap water is only 5. I searched the tank for anything foreign and found two old plant fertilizer stakes and 4 rusted bolts buried in the gravel. Other than that, I'm stumped. My salinity is perfect at 1.010. The PH is a little low at 7.8 and ammonia is 0 ppm. I'm going to not worry about the GH. Ill focus on raising the PH and keep my weekly wc at 25% with distilled water until the GH comes down. The fish don't seem to be stressed and the sores on the Silver Scats are healing fine. Thanks for all the feedback. Let me know if I'm off track.