Perpetually soft water... a blessing or a curse?

[Fallen_Leaves16]

I had several plecos, apistos, and a pair of bettas routinely spawning in a tank where I conducted very small water changes on a sporadic basis; the nitrates were consistently somewhat high, and so was the TDS, but I had few, if any, issues with getting the inhabitants to spawn. I completely redid the tank, added a few more plecos, removed the apistos, and the bettas removed themselves (by violently flinging themselves out tiny openings in the lid onto the floor at odd hours of the night); however, the new loricariid inhabitants produce a large amount of mulm and waste, prompting me to conduct large water changes on a weekly basis. Problem is, ever since I did that, the odontodes on most of the plecos shrunk, and despite the females being visibly fat and gravid, neither the males or the females seem interested in spawning. Even a random pair of common bristlenoses won't spawn anymore!
Now, I'm lucky enough to be living in a region of Piedmont NC with very soft water- TDS of ~70, KH and GH <1. Almost RO params; and I've been able to successfully keep and breed some soft water species without any RO. However, I believe the fluctuations in TDS was a large factor in triggering the plecos to spawn; and now with a consistently low TDS, I guess they just don't want to breed, or something. The increase in water changes was the only change that I implemented- nitrates are now consistently <10ppm, ammonia and nitrite always 0; TDS went from ~200 to <70 (not suddenly, but not exactly gradually, either). I did increase the temp a bit from ~79 to ~82 over the span of a month, but the plecos had spawned after.
Oh, right, and I did put some very lovely oak bark in the tank ~4mos back that I had gotten from a park many years ago; I only have 6 medium-sized slabs, but they release tannins at an astronomically rapid rate; I've never been able to find any of the stuff again. I don't think that was part of the change, though, as the plecos still spawned while the tank was tannin-infused; and I did take out the bark eventually. In the tank are several pairs of Ancistrus, some random Ancistrus, and a trio of L397s. And a pair of juvie Amatitlania nanolutea.
Maybe my fish are all just taking a break from breeding? It's been a fair while since the last batch of eggs, though, more than three months, and the females are quite fat and look egg-laden; they've been like that for a while.
Any tips or advice on why the fish may have stopped breeding? I'm fairly sure it might be the soft water and water changes; any thoughts?

[bekateen]

My L397 breed year round, but they are definitely seasonal in terms of the intensity of breeding. I get more spawns in mid to late summer than I do from October - March.

Your water parameters sound wonderful! What's your pH?

Cheers,
Eric

[Kirin]

Odontode size is generally seasonal in many Hypostominae and I assume most Loricariids, at least those who have large ones. But the common bristlenoses stopping might be a correlation, might just be coincidence.
There are many factors that stop breeding, density does frequently get seen, I suspect nutrition being a big one.
I can't see the TDS effecting much more then hinting to a seasonal change. How frequently did you water change before?
There are some potential negative impacts of tannins but I can't say have been explored enough in fishes.

[dw1305]

Hi all,
Perpetually soft, acidic water is a great advantage, because it is much, much easier to add compounds to water, rather then take them away.

I can't see the TDS effecting much more then hinting to a seasonal change. How frequently did you water change before?
There are some potential negative impacts of tannins but I can't say have been explored enough in fishes.

What are the downsides to tannic, fulvic and humic compounds? I'll pin my colours to the mast and say I add structural leaf litter and Alnus glutinosa "cones" to all my tanks (all rainwater). I don't aim for a "opaque", more weak green tea coloured.

I was of the understanding that they play an important role in regulating ion uptake soft, acidic water: <Dissolved organic carbon from the upper Rio Negro protects zebrafish (Danio rerio) against ionoregulatory disturbances caused by low pH exposure>.

I'm not sure he is still active, but Christian Steinberg carried out a lot of research at Humboldt University on DOC in aquatic ecosystems. Steinberg, C.E.W. (2008). "Humic substances in the environment with an emphasis on freshwater systems". Environmental science and pollution research international. 15. 15-6. 10.1065/espr2007.12.458.

cheers Darrel

[Fallen_Leaves16]

My L397 breed year round, but they are definitely seasonal in terms of the intensity of breeding. I get more spawns in mid to late summer than I do from October - March.

Your water parameters sound wonderful! What's your pH?

Cheers,
Eric

Thanks! My pH hovers somewhere around ~6.3, last time I checked. Not exactly very acidic, but still passably low, IMO.

Odontode size is generally seasonal in many Hypostominae and I assume most Loricariids, at least those who have large ones. But the common bristlenoses stopping might be a correlation, might just be coincidence.
There are many factors that stop breeding, density does frequently get seen, I suspect nutrition being a big one.
I can't see the TDS effecting much more then hinting to a seasonal change. How frequently did you water change before?
There are some potential negative impacts of tannins but I can't say have been explored enough in fishes.

Thanks!
I used to conduct water changes every month or so; then again, I had rather dense plant growth that probably helped keep nitrates down.
Nutrition shouldn't be an issue- I feed the plecos over a dozen different types of pellets and Repashy gels, along with fresh and/or blanched vegetables and fruits on occasion.
Not sure if it's density; there's ~14 plecos in the tank, and five are <5cm juveniles; there's over two dozen pleco caves of various sizes, and large pieces of wood as well.
My pattern of thought was that the TDS change would indicate a change in seasonality; but if the parameters are perpetually kept static, there wouldn't be much to tell of another seasonal change, thus not influencing the fish to spawn; I'm more used to conducting sudden large water changes, or raising the temperature and refraining from water changes for up to three months to trigger a spawn, but I'm not sure if that's a particularly sustainable option here.