Backyard Aquaponics
A place to discuss aquaponics

Hi Guys,

I am new at Aquqponics. I built my own system and started it up about 3 months ago. Since then I added 50 Nile Tilapia. I have Tomatoes, Green beans, cucumbers, and Basil planted in my plating beds. I have been adding Seaweed to kick start the system. My chemicals in the water check fine with the test kit (Ammonia 0%, Nitrates 0%, Nitrites 0%) but my PH is high 8.2. I am using gravel as a planting media. No metal in the water except for a short length of stainless steel pipe. My fish tank has turned really green (algae I suppose) and I have lost 4 Tilapia over the past 6 weeks one by one. Oxygen levels are good. Water temp at the moment is 70. My concerns are the algae, the PH, and losing my fish one by one. These are my questions. Is the algae harmful? If so how can I clean the water up? Is the algae killing my fish or is there something else I need to look at? ? When approximately will my PH go down? Or how can I control the PH?

Thanks... JLMorris

You have 2 options with your pH. You can wait for it to lower naturally or you can lower it yourself. I would recommend leaving it although you may need to add some additional iron. How long it takes to change will depend on what is buffering it that high. What type of media do you have? Did you give it the vinegar test? Often you will find trying to adjust it yourself will result in it lower for a day or so and returning back to its original value.

As for the algae, you want to try and get rid of it. If it is actually algae. If it is just on the sides of the tank it could just be bioslime stuff and that is ok to keep in there. If you have not already, try and remove any source of light hitting your water. Cover the sides and top of your tank and make sure your water levels are not too high.

My tank is buried with no top... I'll work on a top for my tank. I did do the vinegar test on the media and it was alright, My media is a gray white type gravel. I did lower the PH once and it bounced back the next day. Soooo I guess I'll have to wait it out. My entire system is in a green house.

Tilapia eat algae. It is their preferred food source. A ph of 8.2 won't harm them either. There is something else causing the deaths. Salt up. 1-3 ppt should do the trick.

I second Ron's assessment. I run my system at/around 8.2 pH and my tilapia are fine. Tilapia prefer a pH between 7 and 8, but can survive between 6 and 9, or so I've read. pH swings aren't good for the fish, though. I'd still suspect lack of dissolved oxygen is the culprit, but I don't know the details of your system.

How big is your tank? And how is it aerated?

How big were the fish that died?

It is possible that the algae is the culprit and it can still be a DO issue. Unless I'm incorrect, the algae produce oxygen in the sun, but consume oxygen at night. If you don't have enough external aeration, they can deplete the oxygen in the system overnight. You can 'fix' this by shading the tank, but the algae die-off will cause oxygen depletion too and you'll lose a good source of food for the fish. I've been trying to get to green water since I started, but the fish keep the algae at bay. Do you feed the fish or let them eat the algae?

Another possibility is decaying matter on the bottom of the tank. Is the tank bottom fairly clean? Any uneaten food or leaves that have fallen in will consume oxygen as they decay.

Shade the water to reduce the algae, and make sure you have enough aeration. How do you know the oxygen is fine, do you have a DO tester or something?

I have a 1100 gallon tank and have two fountains for aeration and the fish never come to surface sucking for air. People told me that if the fish aren't coming to the top sucking for air the DO is ok.. I had a friend come over today that has two big aquariums and I had 6 more dead fish. He said blotting may be the problem, too much protein or too much feed. He said it happened to his fish. Said that it is the same as a bad case of constipation. What is you guys opinion. I could have over fed I guess if the algae is food also. Sometimes they don't come up to eat. He also said to salt up that salt acts like a laxative... The fish that died have varied in size but seems that the larger fish are not dying. None of my fish are over 5 inches long. The ones that died are 2 to 3 inches. My tank is clean very little debris if any. I run a net along the bottom and don't bring up any trash.

What will the salt do to the plants?

I hate loosing the little fellows...

Most species of fish are just greedy; it's easier to over-feed a fish than it is to under-feed a fish. If you keep feeding them, they will keep eating until something bad happens. (Ever read the Dr. Suess story, "Fish out of water"?) Always use a quality feed, not so much for the sake of the fish, but for the sake of the plants as the fish' solid waste created from the feed breaks down to provide nutrients for the plants, so ordinary gold-fish food is not suitable in most AP applications; use a specialist AQ feed, or for goldfish, many of the better quality koi feeds are suitable, and feed the fish sparingly.

If there is not enough nutrient to support the plants and the fish aren't going hungry, then you've either got too many plants or not enough fish. If you don't want to remove plants, or don't want to add more fish (cognisant of water quality) and/or you cannot feed more, then you'll need to supplement the plant nutrition from another source (seaweed extract, or similar). If you think carefully about the nitrification cycle/nutrient cycle and look carefully at your own circumstances, then you should be able to decide a suitable course of action.

If you think your fish are bloating (getting a fat round tummy caused by an obstructed digestive tract) then feed them a few baby green peas which acts as a laxative. I've never heard of salt as a laxative; salt is generally a tonic for general well-being, to improve the protein slime coat and offset nitrite-poisoning. Salting 1-3ppt for general health is encouraged in many systems (generally harmless to plants), 5-10ppt in the event of parasitic/viral/bacterial infection (will kill some plants, especially strawberries, but most veges will still keep growing), upto 30ppt for very sick fish/systems for short periods (will generally kill plants) Remember the ocean salinity is about 35ppt, so we're talking very small concentrations of salt compared to sea-water. There's lots of posts on the forum about salting a system.

In addition..

Salting serves a few purposes within AP. Salting is not a necessity and there is many members that dont use it at all but it can assist in fish health.

Some fish like barra and trout have an internal salt content and when they are kept in fresh water they burn energy through osmosis to stabilise between the internal salt content and the outside water. Introducing salt limits this transfer thus saving valuable energy that is better used in fighting disease and promotes good health.

Salt assists with the slimey protective coating on the suface of the fish.

Salt can mitigate the effects of toxins like nitrite.

Salt can assist with parasitic and infection issues.

Sorry for my ignorance but I guess ppt means parts per thousand?? Is that in gallons, liters???

Either ppt... is ppt.... it's just the appropriate quantity/volumeement to acheive that which varies... either imperial or metric...

So a gallon of salt for a 1000 gallon system?? Seems like a lot..

Yes, parts per thousand.

1kg or 1000g per 1000L of water = 1ppt
etc


or in 'funny' numbers
2.2lbs or 35.2 ounces per 264 US gallons = 1ppt
etc

so for your 1100 gallon (4100L) tank, if I get my maths right:
1ppt => 4.1kg = 9 pounds or 144 ounces of salt
2ppt => 8.2kg = 18 pounds or 288 ounces of salt
3ppt => 12.3kg = 27 pounds or 432 ounces of salt
etc

Two important things:
1) Your tank may hold 1100 gallons, but how much water is actually in the system? Salt to the amount of water you have, not to how much water there could be.
2) Use non-iodized pool salt, not table salt, cooking salt etc.

Ok thanks... I have a 1400 gallon tank with 1100 gallons of water.