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I have a breeder tank: it's about 150 gallons with a dozen large tilapia breeders in it and isn't connected to a grow bed. there's a rain barrel bio filter.

temperature is around 75-77 ammonia is very low, and I get no readings of either nitrates or nitrites.

The system has been running for three months now and has been doing pretty well, but recently the PH has been dropping below 5. I do partial water changes to keep it from getting too low, but it keeps dropping. I have a sock full of oyster shells in the filter, but based on what I've read on other threads, I'm reluctant to try to manually adjust the PH with something like PH Up without knowing the cause.

The fish seem to be happy, as they keep having babies, but I've noticed some of the fry going belly up when the PH drops too low.

Just in the last few days, the water has become dirty as well. not sure if it's related.

thanks for any help!

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Nah, the rain barrel is just what the bio filter is housed in. I have a whole house activated carbon filter for my water supply.

 

Ok, I'll head to the brew store (time for the next batch of beer anyway) and pick up some calcium carbonate.

 

thanks for the tip.

 

I idea what's causing your low ph? I'm wondering if I need a settling tank to get the solids out

I keep African Cichlids that like hard water and high PH.  The problem I think you're having is similar to the problem I face here as our water comes from mountain reservoirs and the water is delivered at a PH of 7 or neutral, but the water has very little buffering capacity.  If you just let the water sit in a drum, it will drop to less than 5 in a couple of days as the water reacts with CO2 in the air.  Add in fish waste and bacteria activity it'll drop much faster.

The way I handle for my Africans is by combining a short term boost to the PH and buffering capacity and a longer term stability agent.

1) For long term stability, you can use oyster shells, but it never seemed to have that much impact for me.  I circulate the water over coral gravel which is mostly calcium carbonate

3) Baking soda (which I buy at Costco in 5 or 10 lb bags for cheap) is my main go-to remedy.  Mix some in water and add to the water.  Need to do it relatively slowly as it increases both the PH and the buffering.  While it does raise the pH, which the Tilapia would appreciate, it really helps with the long term buffering to prevent PH drops.  In a 150 gallon reservoir for me about 1/2 cup keeps the PH from dropping over time.   Just add some every day and with every water change and slowly bring up the PH.  Fish do not react well (i.e. they die) with too quick a change in PH.  

This is a best guess based on almost no information, but you may have some stratification occurring in your water column where there are anaerobic pockets in your system causing denitrification to occur.  Find any areas that may have little or no water flow or aeration and try to remedy the problem.  If this is the problem, you will see it clear up in a few days and the nitrates and/or nitrites will start to show up again.  You will want to adjust the pH after the problem area is resolved.  If you system is not in a well ventilated area, you may notice a smell as well.

Thanks so much for the feedback. Randall, I think you're right on the money. I retested my tap water (was having problems with my ph meter) and it was coming out very low, so all the water changes were making things worse (and I think the unbuffered water then dropped even further. So I added baking soda (calcium carbonate made the water incredibly cloudy...) to all new water going into the tank to about a PH of 9. So at 5 gallons at a time, i gradually brought the ph in tank from 5 up to about 8. The fish are happy and breeding again. I have two females just starting to release their broods and expect to have 500 or 1000 more fish the nursery by tomorrow.

Izzy, in response to your comment, i've added bubblers around the tank and periodically move the decorations around to try to mix things up too. So both these measures seem to have really stabilized my tank.

thanks again everyone, it's been incredibly helpful.

roe

you may need to clean the filter.  ...oh, never use baking soda. buy some lime or potassium.

I come from the aquarium fish keeping world where PH, Hardness, and Akalinity are discussed ad naseum in article after article.  The best source for understanding all of this chemistry is to google aquarium water hardness and you'll find a million articles.  If you keep African cichlids from Lakes Malawi or Tanganyika you learn what works both for adjusting soft mountain tap water like I have to be basic liquid rock that these fish prefer.  

For short term buffering to a) raise the PH and b) raise the KH to prevent rapid falls in PH baking soda (Sodium bicarbonate) is cheap, safe, and very effective.  I use it all the time on fish that cost upwards of $80 a piece and I don't take risks with these fish. In fact, you can find recipes all over the internet for making your own rift lake mix using baking soda, (sodim bicarbonate), epsom salt (magnesium), and no-salt (potassium).  

General Hardness is a mix of a lot of a lot of salts and minerals  and isn't the same as KH (sometimes called temporary hardness), Best way I've found is to use coral-based materials in the filter to increase the long term GH.  It's a gradual process.  

here's a link to a decent article about this subject: http://forum.practicalfishkeeping.co.uk/showthread.php?t=64622

Tilapia are the ultimate in forgiving fish.  They'll easily adjust to  PH in a reasonable range, but no fish like rapid changes in PH (i.e. they die).  Moderation is the key in all of this.  Personally, I think for them, you only really need Baking Soda to keep the buffering capacity up and prevent swings in the PH.  Anything else you do is great, but not really necessary for these fish.  Depends on how much you want to tinker.

Basically, all the approaches people have said will work, but they differ in how they work and the speed at which they work.  Hope this helps

in case anyone is interested in an update, I recently tested the carbonate hardness and it came out similar to "rift lake levels" which is in the 12-14 degree range (upper end of the test strip chart), and the PH has been stable at 8 or 8.1.  After surfing around various bulletin boards, I am comfortable using baking soda in small amounts with each water change (and the tank has a pound or two of crushed coral and oyster shells to help out). The fish do seem to be incredibly happy now. One of my smaller females just spat out well over 2000 fry. I've never seen such a thing (last seven batches have averaged 500 or so). and they're all happy, no deaths that I can see and they're eating and growing happily. 

Here's a link to some pictures of the fish on the web.

http://losangeles.craigslist.org/lac/grd/3596443120.html

That's great!  I'm glad you got it resolved.  :-)

Roe Sie said:

Thanks so much for the feedback. Randall, I think you're right on the money. I retested my tap water (was having problems with my ph meter) and it was coming out very low, so all the water changes were making things worse (and I think the unbuffered water then dropped even further. So I added baking soda (calcium carbonate made the water incredibly cloudy...) to all new water going into the tank to about a PH of 9. So at 5 gallons at a time, i gradually brought the ph in tank from 5 up to about 8. The fish are happy and breeding again. I have two females just starting to release their broods and expect to have 500 or 1000 more fish the nursery by tomorrow.

Izzy, in response to your comment, i've added bubblers around the tank and periodically move the decorations around to try to mix things up too. So both these measures seem to have really stabilized my tank.

thanks again everyone, it's been incredibly helpful.

roe

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