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Difference in water hardness between tap and aquarium


s_in_houston
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I noticed last night that the water inside of my aquarium was much harder than the water directly from my sink. ~220 vs 143

Is this normal? I thought aquarium water was supposed to soften over time. 

When I conducted the test, it had been a week since I’ve done a water change and 7 hours since I added Thrive fertilizer. 
 

(And I’m currently conducting the tests to see if maybe my water hardness is a factor in what I see as mediocre plant performance.)

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On 6/10/2024 at 1:16 PM, s_in_houston said:

I noticed last night that the water inside of my aquarium was much harder than the water directly from my sink. ~220 vs 143

Is this normal? I thought aquarium water was supposed to soften over time. 

When I conducted the test, it had been a week since I’ve done a water change and 7 hours since I added Thrive fertilizer. 
 

(And I’m currently conducting the tests to see if maybe my water hardness is a factor in what I see as mediocre plant performance.)

Aquariums often acidify over time, but that general hardness will only go down if calcium and/or magnesium are taken up by plants and animals out of the water column, and even then only if those plants and animals are then removed from the tank (plant trimmings, for example). Then you'd be exporting those nutrients.

But otherwise, and unless you're doing fairly large, regular water changes, top-offs will cause hardening over time, since those minerals will remain behind when the water evaporates. Water of 143 ppm goes in, some evaporates, and the water gets slightly harder. Then you add more 143 ppm water, and over time that number creeps up.

You can prevent that with nutrient export from plant trimmings, for example, by regular water changes, or by doing top offs only with distilled or reverse osmosis water.

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On 6/10/2024 at 1:16 PM, s_in_houston said:

And I’m currently conducting the tests to see if maybe my water hardness is a factor in what I see as mediocre plant performance.)

Depending on plant species. that's usually not going to be the case. Most plants will do just fine in harder. mineral rich water. Gh or calcium hardness will not soften over time. the calcium/magnesium doesnt evaporate, so it can actually increase. your kh can actually become exhausted. 

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Okay I’ll look into this. I have a lid so I don’t do top-offs, per se. Or at least not much. I had been doing weekly water changes of around 20-some-odd percent for a long time and decided to be a little bold and daring and change my routine to every other week.* That said, there is always at least a small amount of evaporation.

And after writing this post, I realize there are a few sources of rocks - some aquarium-store-bought rocks (probably slate) and a small amount of Petco gravel. 
 

But I’ll look into the video. Can’t right now. Thanks!

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On 6/10/2024 at 3:09 PM, s_in_houston said:

ome aquarium-store-bought rocks (probably slate) and a small amount of Petco gravel

Slate and aquarium gravel should be inert, meaning they won't add mineral hardness to the water.

Evaporation is the biggest cause of increased hardness in my experience.  That and the super salty water from feeding live brine shrimp, if you don't rinse the brine off the shrimp.  

On 6/10/2024 at 1:46 PM, Tony s said:

Depending on plant species. that's usually not going to be the case. Most plants will do just fine in harder. mineral rich water. Gh or calcium hardness will not soften over time. the calcium/magnesium doesnt evaporate, so it can actually increase. your kh can actually become exhausted. 

Agreed. Plants appreciate mineral hardness and don't do well in water where minerals are absent.  There really isn't much of a relationship between Kh and Gh. You can have both zero Kh and a bazillion Gh. But, plants do like the Ph on the lower side.

 

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On 6/10/2024 at 3:09 PM, s_in_houston said:

And after writing this post, I realize there are a few sources of rocks - some aquarium-store-bought rocks

limestone based rocks will raise your hardness over time. dragon stone, texas holey rocks will raise your gh. the easy way to tell is to drip some vinegar on it. if it fizzes at all, it's limestone based and will raise gh.

 

slate based. granite based, metamorphic rock (basalts) will not raise you gh. sandstone can, depending on what it's been formed from

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even if everything in an aquarium is inert, its normal to overtime have your hardness/minerals increase over tap water. as your water in the tank evaporates and you top off, you keep adding more minerals, as minerals dont evaporate. the occasional water change helps to keep things from getting too out of whack.

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On 6/11/2024 at 11:14 AM, lefty o said:

even if everything in an aquarium is inert, its normal to overtime have your hardness/minerals increase over tap water. as your water in the tank evaporates and you top off, you keep adding more minerals, as minerals dont evaporate. the occasional water change helps to keep things from getting too out of whack.

I use a lid so I only add water when I do water changes. I’ll see where the numbers are this weekend or so and if the change is a big one. Thanks. 

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On 6/10/2024 at 4:18 PM, tolstoy21 said:

Evaporation is the biggest cause of increased hardness in my experience.  That and the super salty water from feeding live brine shrimp, if you don't rinse the brine off the shrimp.  

Hey wait. I do feed my fish brine shrimp every other day. Albeit frozen baby brine shrimp. Now I wonder if that could be the source. 

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@s_in_houston Probably not, but who knows.

I have certain fish, that when I breed them, I need to keep the water super soft and the Ph low. If I spray a turkey baster full of salty brine water into them, the params swing on me after a day or so of doing this.  

Maybe the cubes have an impact? Maybe not? If they contribute brine at all, it should be a negligible amount.

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On 6/10/2024 at 12:49 PM, Rube_Goldfish said:

 

I knew I'd seen a video @Cory did explaining all this with M&Ms:

It's sometimes called "old tank syndrome".

 

Update: It’s not this. My GH rose significantly since I did a big water change on Monday. 

Either something in my aquarium is leaching (even if it’s not “supposed” to) or something I add to the aquarium is causing the problem (another even if it’s not “supposed” to). 
 

It’ll have to be trial-and-error figuring it out. I’ve heard of people having problems with big pet store gravel, which I have in a bag inside my aquarium. I’ll try that first. 

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On 6/13/2024 at 10:08 AM, s_in_houston said:

Update: It’s not this. My GH rose significantly since I did a big water change on Monday. 

Either something in my aquarium is leaching (even if it’s not “supposed” to) or something I add to the aquarium is causing the problem (another even if it’s not “supposed” to). 
 

It’ll have to be trial-and-error figuring it out. I’ve heard of people having problems with big pet store gravel, which I have in a bag inside my aquarium. I’ll try that first. 

That stinks. Good luck figuring it out, though!

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On 6/13/2024 at 10:39 AM, Rube_Goldfish said:

That stinks. Good luck figuring it out, though!

Thanks. The one upside is that I’ve been feeling like *something* is wrong. My plants used to do better than they are now, and I follow all the usual advice. So there’s a glimmer of hope that I can finally resolve the underlying problem. (I‘m no expert but. I would have to think rapidly-swinging parameters are bad for plant life.)

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@s_in_houston have you always had this issue, or have you added something recently? you're looking for something limestone based, or magnesium based. the carbonates are the easiest way to tell. An old junior high science project was to drip acid on a rock and determine its composition. for an acid you can use white vinegar. or concentrated lemon juice. then if the rock bubbles around the acid edges, there's your culprit.

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