If a soft water fish is raised in hard water, would it be okay to not use RO water?

[emeraldking]

Welcome to TFF...
I won't anymore to your questions for there have been already lots of replies...

 

[TwoTankAmin]

I keep softer water fish because my tap is about 7.0 and the tds are low. But I wanted o keep Altum ANgels which are mostly wild caught. They come out of wevry sofy acid water. Wjen I brought in my firstones the Tank was at pH 4.2 and the TDS were between 20 and 30 ppm. I had an RO/DI unit. It was a 3-stage portable 75 gpd unit. It had carbon-->RO-->DI.Agter about 10+ years I just repalced for a 4 stage. I added a sediment filter in front of the carbon module.

I also moved the angels up from the original paramters to 6.0 pH and about 60-70 ppm TDS over 6 months. However, my goal was not to try to spawn them which is extremely difficult and does require very acid and soft water/

Now once again it is important for us to understand that most "rules" in the hobby are simply not universal. In that respect, in terms of can fish adapt the serious changes in hardness, i would offer a bit of science.

Craig, P.M., Wood, C.M. and McClelland, G.B., 2007. Gill membrane remodeling with soft-water acclimation in zebrafish (Danio rerio). Physiological genomics, 30(1), pp.53-60.

Abstract​

Little is known regarding the ionoregulatory abilities of zebrafish exposed to soft water despite the popularity of this model organism for physiology and aquatic toxicology. We examined genomic and nongenomic changes to gills of zebrafish as they were progressively acclimated from moderately hard freshwater to typical soft water over 7 days and held in soft water for another 7 days. Gills were sampled daily and mRNA expression levels of gill Na+-K+-ATPase (NKA) α1a subunit, epithelium calcium channel (ECaC), carbonic anhydrase-1 and 2 (CA-1, CA-2), Na+/H+ exchanger (NHE-2), V-type proton (H+)-ATPase, and copper transport protein (CTR-1) were quantified by real-time PCR. Changes in enzyme activities of gill NKA were determined and protein levels of NKA and ECaC were quantified by Western blotting. Levels of mRNA for ECaC increased fourfold after day 6, with an associated increase in ECaC protein levels after 1 wk in soft water. CA-1 and CA-2 exhibited a 1.5- and 6-fold increase in gene expression on days 6 and 5, respectively. Likewise, there was a fivefold increase in NHE-2 expression after day 6. Surprisingly, CTR-1 mRNA showed a large transient increase (over threefold) on day 6, while H+-ATPase mRNA did not change. These data demonstrate a high degree of phenotypic plasticity in zebrafish gills exposed to an ion-poor environment. This not only enhances our understanding of ionoregulatory processes in fish but also highlights the need for proper experimental design for studies involving preacclimation to soft water (e.g., metal toxicity).

full paper here: https://journals.physiology.org/doi...jkey=0e0761615a8a2d19ae1330103710509d7e03eadb

 

[angiemike6]

I have to admit that when I first started keeping tropical fish I did not consider whether any particular fish needed soft water or hard water. My water is hard at 310 ppm and with a PH of 7.8 is slightly alkaline. When I look at the fish in my tank they are nearly all soft water fish. I believe all the following of my fish prefer soft water - Albino Corys, Bolivian Ram, Cardinal Tetra, Clown Loaches, Common Plec, Congo Tetra, Golden Dwarf Cichlid, Golden Gourami and YoYo Loach. In fact the only fish I have that is okay with hard water are Boesemani Rainbow Fish.

Having said the above all my fish are more than 5 years old. The Clown loaches are about 12/14 years old and my old Common Plec lasted 29 years.

I do regular 40% weekly water changes, only feed 3 times a week, and can't remember the last time I had any disease in my fish.

 

[GaryE]

What has always bothered me about hardness and pH is a simple question. How many ppm of what?

Within those simple numbers we like are different geology, and probably different minerals. So if fish do well in hardwater, what hardens it? Could different minerals have different effects, and could we be comparing apples and oranges without knowing it?

A chemist may come on and blow my question out of the water, but it is something non chemist me has wondered about.

@angiemike6 - your boesemani may be softwater. The lakes they come from have tested anywhere from pH 6.5 to 9.0, so they are fish that adapt easily.