Backyard Aquaponics
A place to discuss aquaponics

I've added a small handful of crushed shell grit to buffer the PH . . . just in case. However the fish and plants look quite healthy so I'm not overly fussed.

I will try and measure the PH mid day on saturday but no guarantees!!
The temperature most probably varies because of where I have the tank situated. At present it is under a north facing veranda with clear roof sheeting. During the day this can reach up to 45 degrees celcius. On the colder nights we open up large bi-fold doors to suck the hot air into the house.
Other than that it is most probably the wierd fluctuations in weather we have been having lately.

Cheers for the posts - I'll post up some growth charts soon.

The system that I was referring too had a slowly downward trending PH over around 6 months. System was running fine, got to PH 6, still ok, then all of a sudden all the fish died, and the water went smelly.

PH tested at 5.8, ammonia and nitrite were high, but not changing. This went on for about a week, with no change in readins.

The system did not recover until the PH was increased to back over 6. It ran fine from this time onwards - nothing else in the system was changed except for PH.

Obviously temperature will play a role in what PH is toxic to the Nitrowhatsits as well.



I quote from this page: http://www.nfkc.info/What%20is%20the%20Nitrogen%20cycle.htm

Temperature

The temperature for optimum growth of nitrifying bacteria is between 77-86° F (25-30° C).

Growth rate is decreased by 50% at 64° F (18° C).

Growth rate is decreased by 75% at 46-50° F.

No activity will occur at 39° F (4° C)

Nitrifying bacteria will die at 32° F (0° C).

Nitrifying bacteria will die at 120° F (49° C)

Nitrobacter is less tolerant of low temperatures than Nitrosomonas. In cold water systems, care must be taken to monitor the accumulation of nitrites. Here again, except for a few people I know that feel nitrifying bacteria can survive in freezing water, science isn’t on their side. If either of them has found some data to the contrary, I’d be most interested to see it.

PH

The optimum pH range for Nitrosomonas is between 7.8-8.0.

The optimum pH range for Nitrobacter is between 7.7-8.2

Nitrosomonas growth is inhibited at a pH of 6.5. All nitrification is inhibited if the pH drops to 6.0 or less. Care must be taken to monitor ammonia if the pH begins to drop close to 6.5. At this pH almost all of the ammonia present in the water will be in the mildly toxic, ionized NH3+ state.

Starting a new system with a PH heading below 6 wont work, and should not be advocated as a good idea. The PH must be brought back up to enable the bacteria to establish a good colony.

Can you remember what the temps were at the time OBO?

OBO - the fact of the matter is that more mature systems have been proven to work well at lower pH levels, though I wouldn't recommend it with new systems.

When researching these things on aquarium sites, there are a couple of things that we must remember:

1. In recent times it has become apparent that nitrobacter and nitrosomonas are not the only bacteria involved in the nitrification process and in fact may not be the primary ones.

2. The ecosystem in a mature aquaponics grow-bed is somewhat different to an aquarium biofilter. It has some of the properties of a soil based system. This means that there are additional microbes, bacteria, fungi and all sorts of stuff (that I do not profess to understand) in action, which are known to assist nitrification at much lower pH levels in a soil type environment.
Maybe one day someone will do some controlled expermiments on it. Would make a good PHD thesis