I would not water plants if you have a salt water tank. I have a fresh water tank and a gold fish pond and I water plants with fish water all the time. Now if you are treating your water/tank/aquarium for disease or fungus I would not water until I had done a couple of 20-25% water changes and filetered with charcoal. know what I mean?

Whoa....wait a minute. You have a freshwater aquarium and you are using "softened water". BAD. Water softeners exchange ions like calcium for sodium. They are common in areas where well water contains high amounts of potassium, calcium, and phosphate. You should not be using water that comes from a water softener for your tank or your house plants. Depending on what types of fish you are keeping there probably isn't any benefit to using that water. If you are keeping soft-water fish like Amazon or SE Asian fishes, bring the hardness and pH down slowly using RO water which contains hardly anything other than water...no ions, of any kind is a good idea. There are essential ions that are displaced with softened water..too much sodium and not enough of the other ions (that are also more responsible for the gray crusty lime we associate with hard water). I would recommend RO water (not distilled or deionized) if you really want pure water for a planted aquarium or discus. If you have Central American or African lake cichlids, the hard well water would be beneficial, since that is what those fisha are accustomed to. Aside from that, you can use old aquarium water to water plants since it contains high amounts of nitrogen (fish waste) and is great for foliage plants. Just make sure its not from the softener!!

bradarmi-I have 2 tanks, a 55 gallon with large SA aggressive cichlids and a 44 gallon community tank with Discus. I haven't had any problems to date, but will take your advise on using my soft water. I just had it installed in October. I know Discus like soft water, but before i had installed the softner, I was using straight well water without any problems. I do 50% water changes everyother week; which makes using RO water difficult and expensive! So if I were to use my hard water from fish tank to water my palms, it would be ok? Even hard water has sodium content does it not?

protemp: If you recently set up a large water softening tank and use the bagged "salt" from the grocery store to soften it, you will have an ionic inbalance shortly. If you purchased your fish locally, then you should mimic the water they were living in at the store..presumably the same as your tap? In any case, RO units hook up to distilled (aka softened) water for extreme water purifaction - taking all disolved minerals like calcium, sodium, and phosphate. Yes hard water has sodium, as well as magnessium, phosphorous, and calcium. What your unit does it replace all of those with sodium, which makes the water "softer" by reducing divalent ions (Ca+2, Mg+2) for monovalent ions (sodium: Na+1). reducing the pH and hardenss of the water, slightly. People use water softening devices to reduce, not elimate, scale and lime (calcium, magnessium, etc.) deposits from municipal water. I would check with a local fishstore and describe what set up you have and see if they can offer alternatives. Since I also have relatively hard water, I do not keep discus, even though I would like to. I would argue that saturation of water with only sodium is more harmful than all the other ions that are naturally found there.

For example, and this is relative to this forum, I was using softened water to water a palm (before I knew what it was) and had a problem with the leaves turning yellow. It was only then that I realized the water was defecient in magnessium and calcium that I was in trouble. So what I do, especially for palms and other big plants, I water with hard water (which has all the essential nutrients and then some) and flush with RO repeatedly to wash away any salts.

Old water from fishtanks is excelent for the garden (except marine tanks!). I use the water from my blood parrot tank on my potted plants and orchids regularly as a weak foliar feed. Even in areas with hard water salt build up shouldn't be a problem.

Adding 1-2 tbs vinegar per gallon of irrigation water helps neutralize the salt content in the soils and helps displace the salts to flush them out. You need to provide enough H2O so that at least 10-15% of the volume drains out, and not into a saucer otherwise the harmful salts get soaked right back in and really do wonders to the osmotic potentials (a.k.a "root burn", high solute concentration means water is diffused out of the roots and into the soil.)

All container soils become more alkaline over time because of fertilizers, so I think it is best to reverse/ prevent this process slowly, also over time.

Also, adding 3-4 oz 3% H2O2 (Hydrogen peroxide) per gallon water helps increase the O2 in the soil. This is what is found in rainwater and why rainwater works so well.

I never thought of using aquarium water on my plants before. Great idea! My grandpa uses lake water on his flowers, tomato plants and hostas, and they grow beautifully.
I have a 55 gallon African cichlid tank that I drain 75% of the way when I change the water, and dumping it down the drain is wasteful, but now i have a new use for it. Thanks for the idea. i like to do anything I can to help save the environment. Not only does it save water, but its better for the plants.

One concern I forgot to ask about, I use crushed coral as a substrate in my tank because Africans like a higher ph level, but would this hurt my palms?

Coral is basically limestone, which will slowly increase pH of soil or water over time but not nearly as quickly or unpredictably as "garden lime".

I'm not aware of any plant, Palm or otherwise, that prefers alkaline water. Some will tolerate it, but in nature, rain water is always slightly acidic. Just because the soils that some plants are naturally found in may be alkaline doesn't mean the water should be.

Treated tap water usually has some salts that raise the pH slightly. It is for this reason that I add vinegar to tap water, to help neutralize it.

All potting soils tend to become alkaline over time due to the cumulative effect of fertilizer salts and minerals found in irrigation water. We growers need to do the best we can to reverse this process. High pH water definitely does not help.

Add some vinegar and hydrogen peroxide to regular tap water. I find it hard to believe that you can show a difference between that and something else, but what do I know? :-)

Someone else posted earlier about Ca and Mg deficiencies. Dolomite, which is cheap and easy to find, is a great addition to a container fertilizing regimen because it is made up primarily of Ca and Mg which is slowly released over time, and doesn't alter the pH appreciably.