一, What makes RAS water quality turbid and what are its effects?
There are three basic categories of things that make the water in the RAS system cloudy:
Suspended particle matter: this includes fish poop, undigested feed, biological flocs, and dead microorganisms. These particles are usually between 0.1 and 100 μm in diameter. Colloidal particles that are smaller than 1 μm make stable suspension systems that are hard to get rid of by letting them settle by gravity.
Dissolved organic matter: This is what happens when proteins, amino acids, humic acids, and other substances break down. It doesn't directly create turbidity, but it can make particles bigger by sticking to them and making light scatter more.
Community of microbes: Nitrifying bacteria, heterotrophic bacteria, and other biofilms stick to the surface of particles, producing biofilms that make the water even more cloudy.
The main way to measure water quality turbidity is by looking at turbidity (NTU). In RAS, turbidity values are greatly affected by things like the rate of feed feeding, the duration it takes for water to stay in the system, and the efficiency of the filter. In high-density aquaculture, if the solid-liquid separator doesn't work well enough, the ammonia nitrogen and nitrite that come from breaking down leftover feed feces will encourage the growth of microbes. This will make the turbidity rise from 50 NTU to over 200 NTU in just 24 hours.
二,The physical process by which light gets through dirty water
According to Lambert Beer's law, light travels through water in a certain way. The depth of penetration (Z) is negatively connected with turbidity (K). There are two basic ways that light is blocked in murky water.
Effect of scattering: Mie scattering happens when the diameter of particles gets close to the wavelength of light (400–700 nm). This makes the optical path bend. The scattering coefficient for particles with a size of 0.5 μm for green light (550nm) is 1.8 times higher than for red light (650nm). This is why murky water looks blue-green.
Effect of absorption: Chromogenic groups in dissolved organic matter (DOM), such humic acid and fulvic acid, absorb ultraviolet light (280–400nm) and blue light (450–495nm) very well, which changes the way spectral energy is distributed.
When the turbidity goes from 50NTU to 200NTU, the penetration depth of 550nm wavelength light drops sharply from 1.2m to 0.3m, and the intensity attenuation rate reaches 97%. This is what experiments reveal. This alteration has three effects on aquaculture organisms:
Photoperiodic disorder: Fish have cone cells in their retinas that are sensitive to certain wavelengths. Turbidity can change the way these cells work, which can mess up their circadian clock. When turbidity is higher than 150 NTU, for example, the gonadal maturation period in rainbow trout is 30% longer.
Inhibition of feeding behavior: A lot of fish depend on seeing where the feed particles are, and when turbidity is greater than 100NTU, tilapia's feeding efficiency drops by 45%, which slows down their growth.
Photosynthesis has limits: In algal co-culture systems, when turbidity exceeds 80 NTU, the photosynthetic efficiency of microalgae diminishes by 60%, impairing the system's ability to remove nitrogen and phosphorus.
三,Main things to think about when choosing Waterproof Led Lights For Aquariums
Because RAS water quality is cloudy, aquarium lamps should be chosen according on the concepts of "penetration priority, spectral adaptation, and energy efficiency optimization." The exact technical path is as follows:
1. Strategy for choosing wavelengths
Red light (620–750nm) can go deep into the water and maintain a 60% penetration rate even when the water is quite cloudy (200NTU). It is best for deep aquaculture ponds that are more than 1.5m deep. For instance, employing 660nm red light in salmon farming can help the fish gain muscle and improve the amount of meat they produce by 8%.
Light green (495-570nm): It doesn't scatter much on particles that are 0.3–1 μm in diameter, and it's best for places with moderate turbidity (50–150 NTU). When growing South American white shrimp, 520nm green light can help them molt more successfully and lower the risk of soft shell disease.
Blue light (450-495nm): It doesn't go very deep, but it can stop algae from reproducing too much. In algal co-culture systems, it needs to be utilized with red light (red: blue=3:1).
2. Technology for controlling light intensity dynamically
Turbidity feedback system: An integrated turbidity sensor and LED dimming module that can change the brightness of the light in real time. When the turbidity goes from 50NTU to 200NTU, for instance, the system automatically raises the light intensity from 2000lux to 5000lux to keep the penetration light intensity consistent.
Mode of pulse lighting: Instead of continuous lighting, short bursts of high intensity (such 10000lux/10ms) are employed. This can go through water with a lot of turbidity and use less energy. The experiment demonstrates that the pulse mode can enhance the growth rate of perch by 15% while decreasing power usage by 30%.
3. Improving the design of the lamp's structure
Anti-fouling coating technology: Putting superhydrophobic nanoparticles (contact angle>150 °) on the lamp body to keep particles from sticking to it. For instance, LED lights that are coated with fluorosilane lose only 5% of their light efficiency after 30 days of continuous use. This is substantially less than the 30% loss of untreated lights.
Layout of the modular array: Make the lighting fixtures easy to take apart so they can be cleaned and maintained regularly. In a circular aquaculture pond with a diameter of 10m, six sets of 120W modular lighting fixtures are installed in a circle. This can make the light more even by 40% compared to the old central lighting mode.
4. An investigation of a typical application case
Case 1: A technique for producing salmon at high density
A Norwegian land-based RAS factory uses turbidity closed-loop control technology to change the LED spectral ratio in real time by measuring the turbidity of the breeding pool (50–300 NTU):
Turbidity<100NTU: Red light makes up 70% of the light, which helps things grow; 100NTU<turbidity<200NTU: Red light makes up 50% of the light and green light makes up 30%, which helps things look better;
Turbidity>200NTU: Red light makes up 80% of the light, and the intensity is raised to 8000lux to keep it from penetrating.
The plan cuts the time it takes for salmon to grow by 20% and raises the pace at which they turn feed into energy by 12%.
Case 2: Crab and Shrimp System for Co-Breeding
A firm in Jiangsu, China, uses a tiered lighting system in a co-breeding pool for South American white shrimp and Chinese mitten crab.
Blue light (450nm) is the most common color on the surface layer (0–0.5m), which stops algae from growing.
Middle layer (0.5–1.5 m): To suit the varied spectral needs of shrimp and crab, green light (520 nm) and red light (660 nm) are alternately shone on them.
Bottom layer (>1.5m): Red light with a lot of power (10000lux) goes through murky bottom water.
This design raises the survival rate of shrimp and crabs to 92% and boosts unit yield by 25%.
