Cory tank stocking advice reqd. 18dh & 7.2ph

[ClownLurch]

Hi.
Just getting back into fishkeeping for the first time since the 90s....and has it changed! New tank arrives tomorrow 765Lx315wx624h. As I now know clownloaches need a much bigger tank I’m gonna need some other small fun packed fishes IE six minimum Corydoras.
So I need to know:
As I don’t want to do any water softening if possible which corydoras if any are suited to an 18dh & 7.2ph water supply?
If none then which have the highest dh range? as RO will then widen my fish stock choices anyway.

The guy at the end of the streets been keeping fish here for 30yrs and hes sure it’s never tested at 18dh yet so I’ll test it when my API dh and kh test kit arrives. I thought the big freshwater kit would’ve contained dh & kh tests but there’s no money to be made that way!

There’s so many contradictions on these figures in books and the internet it’s unbelievable.
Thanks

 

[seangee]

18dGH sounds plausible for Londonish - its about what I read in the Thames Valley. It really is too hard for corys. Having said that I did keep peppers (c.paleatus) before I switched to RO. The problem was their average lifespan was 12 - 24 months so I was having to buy new fish every year. Seriouslyfish.com is usually the most reliable source for species info.

 

[ClownLurch]

Peppered and Pygmy seemed to have highest dh range looking at various websites and books. So we’re already in pole position. Peppered are what the neighbour keeps, possibly for that reason. He never mentioned any problems although we never got into discussion of lifespans.
I’ve not lived here long and it’s the first time we’ve spoken and that was only due to the guy next door pointing him out during a two metre discussion about interests and hobbies.
I don’t really want to go the RO route.

 

[Byron]

I'll answer your question in two phases. First, all species of Corydoras occur in very soft water that is in most cases on the acidic side re pH (below 7) but in a few habitats the pH is in the slightly basic (low 7's) range. If you were to acquire wild caught species the water should be in this range--soft to very soft, in most cases with an acidic pH.

Some species have been tank raised for decades, and these seem to manage somewhat in moderately hard water with a basic pH. The peppered cory, Corydoras paleatus, is one, along with the Green or Bronze Cory (C. aeneus). It really should come as no surprise to learn than these two species are found in the higher range of GH and pH in many of their habitats, which probably accounts for their relative success as hobby fish where parameters are higher than the majority require. Some other species such as C. sterbai and C. panda are now commercially raised and may fare somewhat better than wild caught fish in moderately hard water. Having said that, fish in most cases do not really adapt to water parameters that are significantly different from their habitat waters for which they have evolved over thousands of years. GH is more important than pH here, because the GH directly affects the functioning of the fish's physiology.

Corydoras pygmaeus was mentioned in one post...this species will not fare well in harder water. Very soft to soft, and maybe up to moderately soft/hard is preferred.

@seangee mentioned shorter lifespans for cories he kept in hardish water. This is the issue with all soft water species when kept in moderately hard or harder water. Simply stated, the dissolved calcium in the harder water is naturally assimilated by the fish's kidneys as part of its normal physiological functioning, termed osmoregulation, by which the fish extracts salts and substances from the water that is continually entering its body via osmosis through every cell, and ending up in the bloodstream. This calcium builds up until it blocks the kidneys and the fish dies. This blockage is evident in a necropsy of the dead fish (necropsy is the term for an autopsy performed on an animal).

I do not think any of us can say how the fish may "feel" as this occurs over years. So I'll leave unanswered the ethical questions around this problem. Ian Fuller has been working with Corydoradinae fish for decades, collecting dozens of species in their habitat, and spawning all of them in his fishroom; Ian owns Corydoras World and is one of the most knowledgeable individuals when it comes to these fish. The longest-lived cory in his fishroom lived into its 40 year.

 

[ClownLurch]

Thanks Byron and Seangee. No Clownloach or Corys it is then.
I knew I should’ve asked on here before hunting around for hours on the Internet for a cory that doesn’t exist.
Which leaves me looking for amusing hard water fish packed with so much personality that it’s gonna charm MrsLurch into allowing the 72” that was my plan all along.
Help me out here please!

edit: Tell you what. I’ll ask over on the main freshwater board.