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I just lost 3 tilapia yesterday, and one a couple days before that, out of about 25 in this tank. For the life of my I can't figure out why they died.  They were all about 3 - 4" long and I've had them since mid-December.  pH = 7, Ammonia, Nitrite and Nitrate levels all close to zero, temp - 72 F.  and plenty of oxygen.  A clue to the mystery, though, is that I've lost fish inexplicably in this tank before, and it is the only system we used PVC glue in. Could that be it?  I've included a couple photos from my iPhone...hopefully they aren't as crazy big as they look now!

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So- I've been cycling my system since March 9, with a few fish in right from the start. I finally got my test kit today and am surprised by the results:

Ammonia: 0
Nitrite: 0
Nitrate: 0
High pH: 8.8


I really expected to see signs of bacterial life by now, but our nighttime temps are still quite cool, so hopefully it is just taking a little longer for that reason. I should mention that my pond also has a strong algae bloom happening.

The big surprise is the pH- I guess the pH tester I've been using maxed out at 7.4, and I didn't realize that it was actually higher! I can easily bring it down by adding more rainwater and driftwood though.

I'm working on insulating the grow bed and making a greenhouse type shroud over it to warm it up. Anyone have any other advice on what these test results might indicate? Aloha -- Shawn
Shawn, we will probably need a little more data. How many fish to how much water? What are those cool nighttime temps (I'm betting your "quite cool" in Hawaii are going to be different than our out here in Colorado ;-). Sure looks like there just isn't anything happening in there yet, but you may also be screwed up by that very high pH. My understanding is that for the nitrification process to take place you need to be between 6 - 8.

Shawn said:
So- I've been cycling my system since March 9, with a few fish in right from the start. I finally got my test kit today and am surprised by the results:

Ammonia: 0
Nitrite: 0
Nitrate: 0
High pH: 8.8


I really expected to see signs of bacterial life by now, but our nighttime temps are still quite cool, so hopefully it is just taking a little longer for that reason. I should mention that my pond also has a strong algae bloom happening.

The big surprise is the pH- I guess the pH tester I've been using maxed out at 7.4, and I didn't realize that it was actually higher! I can easily bring it down by adding more rainwater and driftwood though.

I'm working on insulating the grow bed and making a greenhouse type shroud over it to warm it up. Anyone have any other advice on what these test results might indicate? Aloha -- Shawn
Remember to lower PH slowly for your fish :)

Shawn said:
So- I've been cycling my system since March 9, with a few fish in right from the start. I finally got my test kit today and am surprised by the results:

Ammonia: 0
Nitrite: 0
Nitrate: 0
High pH: 8.8


I really expected to see signs of bacterial life by now, but our nighttime temps are still quite cool, so hopefully it is just taking a little longer for that reason. I should mention that my pond also has a strong algae bloom happening.

The big surprise is the pH- I guess the pH tester I've been using maxed out at 7.4, and I didn't realize that it was actually higher! I can easily bring it down by adding more rainwater and driftwood though.

I'm working on insulating the grow bed and making a greenhouse type shroud over it to warm it up. Anyone have any other advice on what these test results might indicate? Aloha -- Shawn
Is it possible you accidentally introduced a poison rock or ornament? Another reason for the unexpected deaths may be spoiled food. Overfeeding is another. Are any of these possible reasons? Did you lose anymore since this post?
A few fish dieing shortly after a move, I would chalk up to stress. Especially if there are no water quality issues or other apparent reasons and no more have died or are showing signs of illness. A bit of salt (between 1ppt and 3ppt) in systems when fish handling or moving is planned might be a good preventative measure to help ease the stress of handling and hopefully sooth the skin and protect the slime coat from the damage of handling.

I know handling is really hard on catfish so I avoid netting or moving fish unless absolutely necessary or if they are to be dinner.

Tilapia are generally much more forgiving of handling and such but it can be hard on all fish and if they were weak for any reason, then they just naturally culled your school for you.

As to the high pH tank. You mention the algae bloom. Do a pH test early in the morning or before dawn if you can and then do another pH test late afternoon or before it starts getting dark. Compare. If the early morning pH is lower than your evening pH then the algae could be causing the swings, try to block light from the tank. If it isn't algae causing the pH issue, figure out if it is just your tap water that has the high pH or if some of your media is causing the really high pH. Limestone can cause a high pH and no amount of driftwood or acid is likely to stably bring down the pH until the limestone is dissolved. Trying to bring down pH with acid while there is a large amount of a strong buffer like limestone in the system is only likely to cause pH bouncing which is bad for fish, plants and bacteria.

If it is just the tap water causing the high pH, then perhaps pre-treating the water before topping up might be a way to go but I don't really have much experience in this aspect. I just know that there is no point in adding acid to a system with a large amount of buffering media.
Yeah- I realized I should have included more info as soon as I submitted my post. Thanks for all the replies already- if bacteria won't colonize at high pH, then that is probably my biggest problem. I actually didn't mention any fish deaths in my post, but there have been one or two comets dead every few days for a few weeks- actually, you might be able to view my spreadsheet log here, that also has temperature and test data.

Current system details:

Fish: 5 Tilapia and three carp/koi (from 8 to 14" in size), and about 15 comet goldfish (3-4"), and about 8 swordtail guppies.

GB Media: washed black cinder- (it's a popular choice here in Hawaii- widely available) GB is about 75 gallons. Compost worms in GB still seem happy.

Pond is about 900 gallons, ferrocement lined, (which has a lot to do with an alkaline tendency, but it shouldn't be 8.8)

Water is rain catchment, and is typically quite acidic (below 6- which is why I went with ferrocement) I haven't been adding fresh water for about two weeks, in order to avoid flushing away nutrients, but I will now (slowly) to clear the algae bloom and stabilize the pH, and then allow the evening rains to trickle in steadily.

Air temps have been cool by any standards: low 40's to 50's for nighttime lows, and no days warmer than 70 yet. Water temp is low to mid 60's. (See the spreadsheet for specifics)

Pump cycle: Flood and drain every 10 minutes, from sunrise to sunset, with a bubbler on same cycle. Sometimes I turn the bubbler on all day on warm days.

Now- I know I need lots more GB, but there should still be enough nutrients to see some bacteria growth- that's all I'm looking for right now. I can flush the pond overnight on a good rain to stabilize any spikes. There are some plants in the growbed- tomato starts are yellow with spots, but carrots and squash so far look happy. Lettuce was just put in days ago, so time will tell.

Should I extend my pump cycle further into the evenings to make sure the bacteria are getting enough nutrients? Do you think my air temps are too cold for the bacteria?

I do plan on salting for a few weeks, as the fish have been flashing and rubbing (i.e., parasites suspected), but had to special order the salt and it takes a week or two. I think thats all I can think of. Let me know if anything seems totally wrong, shocking, or completely bass ackwards. (Fish pun). Thanks!
Shawn, by my calculations you have maybe 20 lbs of fish for a 900 gallon system - do I have that right? This means that you have 1 lb of fish to every 45 gallons of water, which, combined with the high pH is my guess as to why you aren't seeing much nutrient activity yet. Starting stocking density I'm familiar with is close to 1 lb of fish every 5 - 10 gallons of water. Problem is, given the small grow bed if you start increasing your stocking density you aren't going to have the beds to support it. Is there a way you can sub-divide your pond into something more appropriate for the bed (70 - 140 gallons) and move all the fish over there?
Well- I was concerned that I don't have the GB volume that would be required for that kind of fish density. I have more GB's coming eventually, but for now I'm just tying to maintain just enough of a balance that my 75 gallons of GB can handle what I do have. Two half-barrel beds are being constructed now, so soon I'll add in another 50 gallons. I'm thinking I may need to increase the pump time, to wash the system with more nutrients, but I need a better overflow pipe fist.

I've seen some data online that indicates Nitrisomonas bacteria like a higher pH- up to ' mid eights', so maybe I'm not all that too alkaline after all...

Sylvia Bernstein said:
Shawn, by my calculations you have maybe 20 lbs of fish for a 900 gallon system - do I have that right? This means that you have 1 lb of fish to every 45 gallons of water, which, combined with the high pH is my guess as to why you aren't seeing much nutrient activity yet. Starting stocking density I'm familiar with is close to 1 lb of fish every 5 - 10 gallons of water. Great excuse to buy more fish!
Shawn, your pH is high but time and patients may take care of that.
How new is the concrete pond?

I would not up your stocking beyond what your grow beds can support. Plan perhaps 1 fish per 5 gallons of flood and drain media for the time being.

Problem is, if you are getting algae, then it may be using up all the ammonia before your bacteria really have much chance to establish. If you can shade all water tanks as completely as possible, that can help get you past this initial challenge.

I must admit, I've normally cycled up new systems fishlessly so I could safely dose with an ammonia source to get cycling started. However, since your pH is so high and you have fish in the system, you don't want to see much ammonia at all as at that high pH ammonia is really toxic for the fish.

The fish and bacteria usually don't mind a high pH (provided the ammonia levels stay really low.) With the high pH the plants are most likely to show problems with nutrient lock out of things like Iron.
Thanks TC- I will try to test the pH algae spike soon, but last night we had a few inches of rain so I let the pond flush all night- cleared the algae out by 50%, so the water is nice and clean and pH dropped to 8.2, but we'll see if the algae wants to come back on strong right away, or maybe the GB will start to control it...

TCLynx said:
Shawn, your pH is high but time and patients may take care of that.
How new is the concrete pond?

I would not up your stocking beyond what your grow beds can support. Plan perhaps 1 fish per 5 gallons of flood and drain media for the time being.

Problem is, if you are getting algae, then it may be using up all the ammonia before your bacteria really have much chance to establish. If you can shade all water tanks as completely as possible, that can help get you past this initial challenge.

I must admit, I've normally cycled up new systems fishlessly so I could safely dose with an ammonia source to get cycling started. However, since your pH is so high and you have fish in the system, you don't want to see much ammonia at all as at that high pH ammonia is really toxic for the fish.

The fish and bacteria usually don't mind a high pH (provided the ammonia levels stay really low.) With the high pH the plants are most likely to show problems with nutrient lock out of things like Iron.
Hey folks, anyone got any great and inexpensive ideas on lowering the ph in my pond. As I have said in the past our tap water is very high in PH. I just tested my pond again and it is still in the 9.0 area. In the past I have bought some PH lowering acid, but it is very expensive and with about 4000 gallons it won't be cheap to keep it in range. I have tried adding some spagnum peat moss to help lower it over time, but it just isn't working. I am getting nutrient lockout for sure. A lot of my leaves are pale yellow and surely aren't getting enough iron. I need a reasonably priced fix if anyone has it!
Thanks
I saw a system online that used bailed pine needles to lower PH in a concrete pond/aquaponics setup. It was a large system and the bail was the size of hay bales. According to his experience it worked well.

Good Luck with getting it down :)

Jeff Givan said:
Hey folks, anyone got any great and inexpensive ideas on lowering the ph in my pond. As I have said in the past our tap water is very high in PH. I just tested my pond again and it is still in the 9.0 area. In the past I have bought some PH lowering acid, but it is very expensive and with about 4000 gallons it won't be cheap to keep it in range. I have tried adding some spagnum peat moss to help lower it over time, but it just isn't working. I am getting nutrient lockout for sure. A lot of my leaves are pale yellow and surely aren't getting enough iron. I need a reasonably priced fix if anyone has it!
Thanks

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