Fish Stressed


Junior Poster
Jun 30, 2006
After 50% water changes, all of the fish are showing signs of stress, such as rapid respiration. I am currently using the EI index for dosing ferts and traces as well and injected CO2. Any idea as to what is causing this? The local fish guy thinks it might be a ph swing? My setup is as follows:

29 gal
3.5 watts per gal lights on ten hour timer
eheim canister filter
Pressurized CO2 on one half hour before lights and off one half hour before lights out.

SpongeBob SquarePlants

Prolific Poster
Dec 11, 2006
Are you using tap/hose water to refill the tank?

I noticed this once when I did a water change. So here's what I do and the fish seem happy. I drain 50-60% of the water from the tank (130 gallon), do my pruning and cleaning like normal. When I refill the tank, I use regular hose water from outside. When the tank is at about 75% full I add 2 caps (20ml) of Auquasafe de-chlorinator and 2 caps (10ml) of Prime. Then continue to fill the tank slowy. When its topped off I add the remaining de-chlorinators & ferts etc. The fish are as happy as can be.

I have a PinPoint PH controller, which I used to use to control the CO2 but now its just running as a reference check to give a "general" idea of the PH. My PH will read as low as 5.99 during the day and go up to 6.4 at night, but after a water change the PH can be up towards 7.00-7.20 I run the CO2 on a timer now and not the PH controller, so after a water change it only takes a few hours for the PH to get back in line with the CO2 running full blast. (full blast is where I'm able to unject as much CO2 as possible without the fish complaining)

Anyway, it seems like by adding some water conditioner to the tap water during refill the fish remain calm and relaxed. When the tank is full you would never know I just did a water change, aside from the PH reading. The fish have no problem eating when I do an afternoon water change also. I have Discus eating from worm cups + Rams, Loaches, and other little fishes.

PS. I need to shoot some pictures of my tank and post them with a tank-bio/info, since I've been following the advice from Tom and others on there my tank has been flourishing. I have no algae, crystal clear water, O2 pearling, happy fish and I spend 1 day a week doing maintenance which takes 30-45 min.

Tom Barr

Staff member
Jan 23, 2005
If the swing is due to the CO2 injection, this has no effect at all on the fish.

Their blood is loaded witgh CO2, just like ours and the gills exchange the CO2 for O2.

pH shifts due to salts, eg, adding a lot of baking soda or removing it rapidly etc, these can cause pH shifts, but the death/stress is not due to the pH, it's do to osmotic shock.
Sort of like tossing a fish into salt water or from salt water to freshwater.

Add some dechlorinator as you are filling the tank.
Otherwise make sure the temp is the same upon refilling and if you have not done many water changes prior, sometimes fish are stressed, but more water changes tend to make the tank very stable and then you can do large, 80-90% water changes without issue if you want.

I have altums, rare SA soft water fish etc, I do huge weekly water changes for them and have done 50% or close for about 30 years and I have a long list of fish I've had without ever a disease, never needing medications, having bred about 20or so species etc.

I have clients with perhaps the entire net worth of the LFS's livestock in their tanks, I do 50-70% water changes weekly without issues.

So have most everyone that does EI and have for many years now.
So it's something else you are overlooking, not the water change or pH.

Get a tap water report also, that can help in many cases and is a wise idea.
Tom Barr