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Why is my (soft) tap water becoming hard in the tank?

no_robotocha

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New to this and new tank - after weeks of prep, finally have neon tetras in.

Testing the water, all seems fine except for the water hardness, which is measuring at the hardest on the scale (180).

We tested our tap water and this had a very soft measurement (20).

We now have a new tank filter installed and some other measures to take (not re-tested yet) - but does anyone know what factors may be causing this issue?

Thanks in advance!
 
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Byron

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Probably there is some calcareous substance in the tank. This refers to rock, stone, gravel/sand, shells, coral, which are all composed of calcareous mineral, most usually calcium although magnesium is often included. These items will slowly dissolve, adding calcium/magnesium to the water, thus raising the GH.

Rock/substrate made from limestone, marble, dolomite, aragonite, and/or crushed coral can all do this.

Water is one of the most soluble substances on the planet, so it readily assimilates minerals and organics with which it comes into contact. This is what gives water its degree of hardness.
 
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no_robotocha

no_robotocha

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Thanks for the response Byron - that being the case, should I be looking to remove these elements (as the recommended water hardness for neon tetras is considerably lower than my reading)?

As the filter has been added it may reduce levels but I don't want to endanger the fish..
 

Byron

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Thanks for the response Byron - that being the case, should I be looking to remove these elements (as the recommended water hardness for neon tetras is considerably lower than my reading)?
As the filter has been added it may reduce levels but I don't want to endanger the fish..
The filter is not likely to reduce the GH. Assuming there is something calcareous in the tank, it needs to be removed. If all objects are inert the GH of the source (tap) water will remain basically the same in an aquarium, though it may lower depending upon initial levels and organics. But that would not bother soft water species.

Can you think what might be doing this? Are there any rocks/stones? What is the substrate material?

What is the media in the filter? This can increase hardness if again there is something calcareous dissolving, though that is unlikely the issue here from what you've posted, but it is worth pinning down. Water chemistry is a very complicated business, because one factor can affect others; keeping things simple is always safer.
 

AtomicFish

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Depending on where you live some cities water is naturally hard or soft. Where I am we have very hard water. For soft water to become hard like you described you would have to have something in your tank making it do that.
 

Kritastrophe

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How frequently do you do water changes? As water evaporates it leaves behind the minerals/metals/etc and could (over a time period) slowly be raising the gh in the tank. I don’t think this would be the main factor (unless you just aren’t doing water changes and are topping off the water with significant water loss over time due to evaporation). Another option is does your house use a membrane tank? If so it could be old and breaking down. One other thing to consider is if your water comes from a public well/wells the water softness/hardness fluctuates if it rains a lot as sediment is disturbed and washed in. I would put tap water in a glass let it sit overnight and retest gh.
 

Byron

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I just noticed the last post before yesterday in this thread was in March, so the OP is probably no longer following. :huh:
 
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