pH Has Increased Since Adding Fish

[Roger]

I had a quick question I was hoping someone could shed some light on.  I've cycled my system over the last 7 weeks and last week decided to introduce fish.  Water tests confirmed that by biofilter was successfully removing 30ml of ammonia from my 100 gallon FT on a daily basis.  Nitrites at zero after 24 hours as well.  Nitrates still high (about 100ppm) but I've read these will go down the bigger my plants get and that it isn't a huge concern for fish as long as the high nitrates don't stay that way indefinitely.  Water temp is about 75 degrees and pH was staying right around 7.1.

I added 20 two to three inch blue tilapia to my FT 3 days ago.  The fish have been doing wonderful and seem to be under no stress.  I feed small fingerling pellets once a day for about 5 minutes.  My concern though is that I've noticed the pH continually raising over the course of the last few days.  As of today it read 7.9.  Upon taking this reading today I added about 20ml of General Hydroponics pH down.  From past experience this should lower the pH by about .2 parts.  I've ensured not to make any more of a change in pH by adding more pH down as I know fish don't handle pH swings particularly well.

I was curious if anyone else has experienced something similar when adding fish.  It seems that in the past I've been told by a few members here that the pH would begin to drop once fish were added.  Any advice would be helpful.  I'm off to a great start on my first system and would like to keep it that way.

[Jonathan Kadish NYC AA Chair]

My only advice is patience ... no sudden moves. I wouldn't be concerned yet, but if it keeps climbing then you need to find the source. It can really only be one of 3 things - top up water, media or the tank is made of concrete. Let your system find a balance. In the beginning it is all about the fish and the bio-filter, and as your system matures you should find the PH begin to drop. That will take some time.

[Roger]

Thanks for your advice Jonathan.  I will take your advice and just continue taking water samples everyday.

Jonathan Kadish said:

My only advice is patience ... no sudden moves. I wouldn't be concerned yet, but if it keeps climbing then you need to find the source. It can really only be one of 3 things - top up water, media or the tank is made of concrete. Let your system find a balance. In the beginning it is all about the fish and the bio-filter, and as your system matures you should find the PH begin to drop. That will take some time.

[Roger]

Two days later = all tank setup the same.  Ammonia = .25, Nitrite = 0, Nitrate = 100ppm, pH = 7.6.  pH seems to have lowered but lost one fish and for the last two tanks fish have been staying near bottom of FT and not eating quite as well.  I've cut back on feeding since.  

-What is the ideal pH range to keep the plants, fish, bacteria happy?

-Do the fish need light?  Right now I have them covered with plywood b/c they kept jumping out the first day I introduced them to the FT.

-I never got my nitrates down to 0ppm.  Does that matter?  I thought fish could sustain higher levels of nitrates while your plants established themselves.

Sorry for all of the questions.  Right now I've noticed the fish haven't eaten like normal for the last two days and am just curious as to what is happening.  I'm mainly concerned with the pH and nitrate levels.  Thanks for any input/advice anyone can provide.

[Jonathan Kadish NYC AA Chair]

1) PH of 7.0 considered the best of both worlds... fish/plants. If you get down below 6 then you run the risk of crashing your bio-filter. If you are up in the 8s then certain minerals become unavailable to plants and depending on the species of plant they will show deficiencies.

2) Yes fish need a day/night cycle. A window near by would do it. Get some netting to put over the tank to keep them from jumping.

3) The way you get your nitrates down is have more plants, or/and feed your fish less. Very high nitrates may inhibit the growth of your fish but they should tolerate it.

Fish are very efficient creatures and being cold blooded they only use food for growth and movement. They can go weeks with out food as a way to alter the water chemistry in your system.

[Roger]

Very good info Jonathan!  I have quite a few plants, and have added plants, but nitrates are testing above 100ppm.  I have one bush tomato plant, two cucumber, some sage, kale, sunflower, and two ornamentals...Fish do seem happier tonight though and no dead ones!  Twenty out of twenty two....not too bad I guess for the first week.