impart of soft water on tank?

[jgorden]

Newbie here! I got a 28 gal tank Mother's Day 2004 and have really been enjoying it. I posted this on the general topics board, but apparently no one had an answer. :( Hoping someone here does!

We got a water softener installed 2 months ago and I'm wondering what effect it will eventually have on the tank. Our water before was VERY hard (off the scale) and now the aquarium is just starting to register between very hard and hard on the test strip. Obviously, this trend will continue until I eventually have very soft water in the tank. Anything I should worry about?

Thanks!
1 male betta
3 zebra danios
4 rasboras (heteromorpha)
2 golden twin-bar platies (one of which I have just discovered by reading this site is pregnant and delivery is imminent) :)
2 dwarf platies (much less poop than the full size models!)
1 panda cory (his 3 friends didn't make it, but he's still very happily hanging out)

[RTR]

The hardness changed by the water softener (salt exchange, right?) is mostly calcium and magnesium ions, so will not have that much direct effect on the fish. But the total dissolved hardness (TDS, a measure of all the ions in solution in the water) will actually be higher in the post-softener water. The osmolarity of the water will be greater even than it was before.

In a planted tank, the high sodium levels might cause some issues with uptake of other ions such as the calcium and magnesium already mentioned. For fish-only, the effect will not be large.

[jgorden]

Thanks. Yes, it's a salt exchange softener, and I don't have any live plants. I'm noticing that my pH (which was low before) is slowly going up as the hardness comes down. I've heard that soft water is more prone to shifts in pH that can be detrimental to the fish. So, that might be the only thing I need to worry about? The pH is actually only normal now, but if the trend continues I assume that won't be good.

[RTR]

Strange though it may sound, especially on the boards where so many folks fret over pH routinely, pH itself is not particularly important for aquarium keeping, especially FO. Fish do not and cannot "read" ph. What is impotant is total dissolved solids (TDS) which in effect measures osmoloarity, and the stability of that. Fish to be maintained (not bred) in a community tank are largely quite adaptable to water conditions, provided that changes in conditions are done gradually. Sudden changes can have poor to bad effects.

Certain fish, especially blackwater fish such as certain Tetras and dwarf Cichlids, do need low TDS water to breed successfully. Their eggs (not the fish themselves) are quite sensitive to both the quantity and nature of the minerals in the water. To breed these readily, you do need low TDS water, which is "soft" and acid, but it is the mineral content and the particular minerals absent which affect this, not the pH itself - which will be low.

With your salt exchange water, your GH will read lower, your KH may or more likely may not. You would be better to monitor those than the pH, but once stablized, the pH measure is faster and easier. Your TDS after the water softener will read lower GH (Ca++ & Mg++ have been swapped out for Na+ ions), but the TDS will be higher, so higher osmolarity. As this is happening gradually with partial water changes, the fish will likely not notice.

You have to be very careful saying soft water, and be very specific. GH does not in and of itself affect pH at all. KH, or better called alkalinity, does largely control pH so long as "buffers" or acids (CO2) have not been added. In the wild (untreated water), waters high in GH tend to be high in KH as well - the calcium and magnesium salts present are frequently carbonates or bicarbonates, and is the buffering system for most native water in the world. Low GH water is "soft" for laundry purposes (lacks high Ca++ and Mg++), but that says nothing about what the pH will be, or what the TDS/osmolarity is. Low KH water is also called soft - and would have a low pH. High GH water may or may not be high KH in processed water, but normally is in the wild. The two different hardness factors tested tend to be at least roughly comparable in the wild, but may not be at all in public processed water supplies. For processed water you have to test at least GH and KH to have any idea what is happening.

This gets very technical quickly - if it is too hard to understand, let me know.

[jgorden]

Thanks (my biology degree with other science background allowed me to pretty much follow that! I appreciate the time you took to respond.)

I'm just glad the answer was not "you're going to kill all your fish within 2 months". :)