Are Large Water Changes Killing Fish? Small vs Large Water Changes -

  • We are currently upgrading MFK. thanks! -neo
frequent water changes, 60-70% every 3 days in a 3ftx1.5ftx1.5ft tank stresses my flowerhorn and he gets fin rot. noticed it twice in 2-3 weeks.... when i increase duration to 5 days no such issue... sadly he has HITH now and is being isolated

rest of fish no issue..
 
Bacterial (or fungal) infections such as fin rot, are not caused by adding fresh water to a closed system. Designer fish such as FH are often genetically weak fish and can be more prone to health issues.
 
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RD. said:
Bacterial (or fungal) infections such as fin rot, are not caused by adding fresh water to a closed system. Designer fish such as FH are often genetically weak fish and can be more prone to health issues.
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My thinking that if the PH differs dramatically between the tank and tap water some sort of PH shock could happen. Tapwater here comes out at 9.0 and settles at 7.4, surely this drop could shock fish? Also depends on the amount of co2 gassed into our water...
 
pH changes do not cause shock of any kind. Another misconception in this hobby that seems to get passed from generation to generation. The change that is associated with "pH shock", is a change in TDS, which can cause osmotic shock, but that generally won't happen with a partial water change, even a 60-70% water change, and typically is only a serious issue when going from high TDS, to low TDS.
 
RD. said:
pH changes do not cause shock of any kind. Another misconception in this hobby that seems to get passed from generation to generation. The change that is associated with "pH shock", is a change in TDS, which can cause osmotic shock, but that generally won't happen with a partial water change, even a 60-70% water change, and typically is only a serious issue when going from high TDS, to low TDS.
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Ah. Just had a look and this makes sense, we want to pull out a TDS meter not PH kits when acclimating. This is interesting :)
 
Hendre said:
My thinking that if the PH differs dramatically between the tank and tap water some sort of PH shock could happen. Tapwater here comes out at 9.0 and settles at 7.4, surely this drop could shock fish? Also depends on the amount of co2 gassed into our water...
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article on how much tolerance fish have with PH changes, start at page 5

https://www.waterboards.ca.gov/rwqcb5/water_issues/basin_plans/ph_turbidity/ph_turbidity_04phreq.pdf

A technical review of the effects of rapid pH changes on benthic macroinvertebrates revealed evidence indicating that macroinvertebrates rapidly exposed to pH changes of one unit or more, when pH is maintained within the 6.5 to 8.5 range, would not experience mortality, or other long-term adverse effects.
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Thanks for that, Rocksor. I guess what I should have said was - reasonable pH changes do not cause shock of any kind. I would have liked to have seen the TDS stats in that paper, but their findings pretty much mirror what I have seen over the years. Wild caught fish from their native SA/CA/African/Asian waters coming out of a bag full of pizz, where the ammonia levels are sky high, hence pH pushed down to god only knows what value, and going directly into holding tanks with a pH of 8.0. No issues with the vast majority of species. A FH should not be affected at all, unless the owner was going from one extreme to another extreme.

From that paper .......

"The ability of fish to rapidly acclimate to waters having substantially different pH values is further demonstrated by hatchery stocking programs and the freshwater tropical fish (aquarium) industry, where it is common to move fish from one water body or aquarium to another that differ by at least 0.5 pH units, and often by more than 1.0 pH unit. However, it should be noted that this "stocking" of fish typically involves waters with pH values in the range of 6.5 to 8.5 units so that the fish are transferred to waters with pH values well within the range that is physiologically acceptable to them."
 
I have a 20 gal tank with a 3'' inch fish in it so I do a 25% water change like every other day
 
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