# How critical is Hardness



## dean (6 May 2017)

Hi not sure if this is right place to post it but how critical is water hardness ? 



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## three-fingers (6 May 2017)

Critical for what though? 

For myself, with soft water, I find it is critically important to add GH booster in order to avoid spinal/fin deformities in guppy fry and also to avoid potassium deficiency in certain fast growing stem plants like _Hygrophila polysperma.  
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If I wasn't breeding hard water fish like guppies and used less light over my tanks to reduce nutrient demand (or just dosed more macros like full EI) it wouldn't be critical at all and I would just use straight tap water.

Basically, it depends on what fish and plants you are keeping. Generally, it is not critical at all for plants, there are some species that do better in hard water due to the extra nutrients, but if you dose EI these extra nutrients are redundant. Many true aquatic plants like _Vallisneria _spp. can use carbonates in the water as a carbon source, so it could be a critical factor in low-tech tanks with such plants, but if you inject 30ppm of CO2 then carbonates are also kinda redundant.  Some people (and many old books/sites) still maintain that a few certain species of plants require soft water - however experts like Tom Barr can show you beautiful tanks full of such species thriving in rock-hard water, so IMO it is a myth that soft water is needed for such plants.

Many hard water fish simply won't live healthily in soft water (they can develop mineral deficiencies), and many wild-caught soft water fish don't adapt well to very hard water (but tank/farm bred examples are usually fine).

I see many people trying to soften their water with RO for some reason. RO is great as it is more pure than tap water, but more most high-tech tanks, you would be better off just sticking to hard tap water, _especially _if your not dosing full EI.  The best reason I've seen for using RO on a high tech tank is to reduce limescale build up if you have a rimless tank and very hard tap water.


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## dean (7 May 2017)

I have concrete hard water it's great for breeding tanyanikan cichlids but I do struggle with some plants 


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