Do I really need a chiller for my planted aquarium?

Introduction

Fish tank temperatures can vary widely. In temperate countries it is not uncommon to see unheated tanks reaching 18 degrees Celsius (64 F) and below, and in the tropics it is common to see tanks without a cooler reaching an intra-day high of 32 degrees Celsius (90 F) or more.

In temperate countries, the environment is often too cold for tropical tanks and hobbyists will purchase a heater to raise tank temperatures. The situation is reversed in the tropics, where tank temperatures are too high, and people often use air-conditioned rooms or chillers to lower tank temperatures.

While heaters are cheap, chillers are very expensive and bulky. A chiller for a tank of the same size costs about 10 times more than a heater. So it is cheap and relatively easy to raise tank temperatures, but quite expensive to lower them. For temperate countries with summer temperature spikes and tropical countries with high temperatures all year round, buying a chiller is a serious decision. So is a chiller really worth it?

How high is high?

For most tropical planted aquariums, 22-26 degrees Celsius (72-78 F) is the sweet spot where planted aquariums are easy to manage. There isn't much difference in operating within the sweet spot. Every degree Celsius above this range adds significantly to the list of pros and cons. Keeping below 26C is only a few degrees lower than the average temperature in the tropics (between 27-32C), but it does make a significant difference in some respects.

Below are comparisons of different plant species grown at two temperatures: 31C and 24C. We have used similar light, substrate and fertiliser regimes for both plant samples.

Comparing plant growth forms at 31C vs 24C:

Bacopa salzmannii SG grown at 31C (left) and 24C (right). Exhibits smaller leaves and a fully green stem when grown at warmer temperatures. Leaf colouration is also stronger in the cooler tank.

Myriophyllum 'Golden' grown at 31C (left) and 24C (right). This plant shows a whiter colouration at cooler temperatures under similar light and nutrient regimes.

Rotala macrandra mini type 4 grown in 31C (left) and 24C (right). The plant grown in cooler conditions shows redder coloration and fuller leaves.

Plants that require nitrate limitation to produce a redder colour are more likely to do so at cooler temperatures. Limnophila aromatica is such a plant. Here it is grown at 24C (left) vs 31C (right) under similar dosage regimes and light levels. The plant grown in the cooler tank is more likely to develop a redder colour.

A few degrees Celsius difference can have a significant effect on the shape and colour of a plant for people who are very particular about how their plants grow. However, this does not mean that a warm tank cannot grow red plants well - just that the hue of certain species may not be as deep compared to plants grown in a cooler tank.

There are also many species such as Alternanthera reineckii which has a consistent beautiful red colour even at higher temperatures. This batch is grown in a 31C aquarium;

Many species will continue to grow well at higher temperatures as long as CO2 levels and nutrient requirements are met. Several Eriocaulon species can grow well into the 30s. Most carpets do well, although HC prefers cooler temperatures. Alternanthera, Hygrophila and most common Rotala & Ludwigia species will do well into the 30s. The above tank hovers around 30 degrees Celsius.

Higher temperatures = increased difficulty?

Higher temperature pros (+) and cons (-):

• Faster plant & microbial metabolism  (+/-)
• Tanks mature faster (++)
• Plants grows faster if growth conditions are good (+/-)
• Plants deteriorate faster if growth conditions are poor (--)
• Algae grows faster (- -)
• Harder to tune CO2 (plant metabolism is high, CO2 solubility is reduced) (-)
• Poorer color and growth form for some species (-)
• Stunts cold water species (-)

There are actually some benefits to warmer temperatures. Plant and microbial metabolism is increased when temperatures are higher. Tanks cycle and mature more quickly. If well managed, a warm aquarium can skip new aquarium algae problems and complete the aquarium cycle faster than a cooler aquarium.

Aquatic plants grow faster in warmer temperatures, with greater demands for growth inputs such as nutrients and carbon dioxide. Aquascapes can grow and mature much faster in warmer tanks if the plants are given what they need to grow. Aquascapes can be established and mature much more quickly in warmer tanks, provided the plants are given what they need in terms of nutrients and carbon dioxide.

On the flip side, algae also grows much faster in warmer tanks and runaway algae problems are more difficult to deal with than in cooler tanks. When things go wrong in a hot tank, they go wrong more quickly - plant dieback due to poor parameters and algae problems both happen at a rapid rate compared to a cooler tank. Aquarists have less time to react and this has a severe impact on newer, less experienced aquarists.

For less experienced aquarists, runaway algae problems often become the dominant issue and heat is often blamed for the failure of the entire tank.

Managing algae in warm tanks

Is it more difficult to control algae in warm tanks? Yes, in the sense that algae will grow much faster if given the opportunity. However, if managed well, a warm tank can be as algae free as a cool tank. This will come as a surprise to people who have always struggled with algae in a warm tank.

In the 2hr Aquarist gallery we have a number of specially heated tanks that we run at 31-32C (as above) to test how heat affects plant growth forms and product performance. The concepts that make a warm tank algae-resistant are not too different from a chilled tank.

Hot tanks are more vulnerable to instabilities

Hot tanks can be more unstable - decomposition and deterioration happen more quickly, an ammonia spike from overfeeding, for example, which triggers algae, will hit a warm tank harder than a cold one. Running out of CO2? The decline in growth and the algae spike will hit harder and faster in a warm tank than a cold one. Lights left on too long? The algae spike will occur faster in a warm tank than in a cold tank.

All this means that we need to run our warm tank with extra sensitivity. There are a few key points that can help with this:

• Plant density provides stability. The best defence against algae is a densely planted aquarium where the plants out-compete the algae. Plant densely at the start and also trim and remove old growth to make room for new growth. Warm tanks grow in quickly and can easily use plant dominance to deny algae a home. Get this right and there is much more room for error in other areas

• Make sure your CO2 injection is rock solid. Use inline diffusers or reactors and stay away from in-tank diffusers, which clog more easily and provide poorer CO2 dissolution. Fluctuating CO2 levels cause a lot of reprogramming in plants and are the main cause of many algae problems. Good CO2 levels allow tanks to outgrow many problems.

• Aim for low bio-loads. Low bio-load, high plant mass results in more stable ecosystems.

• Clean water surface and good flow pattern (aim for 6x to 10x filter turnover) to ensure good oxygen levels and microbial balance in the tank. The overall biological stability of the aquarium is highly dependent on these two factors together with adequate surface area for microbial colonisation (adequate filter media + substrate zone).

• Bio-active aquasoil substrates contribute more to the biological ecosystem than inert gravel. When using an inert substrate, a grain size of 2-3mm works better than coarse pea gravel, which does not work well in planted tanks. Aquasoil substrates also allow you to move nutrients into the substrate zone, see more below.

Dust algae on glass ? Moving N/P into the substrate

Green dust algae is one of the most common problems in warm tanks. In fully planted tanks, plant dominance usually sets in as the tank matures and the dust algae will clear itself as the tank is fully occupied by plants. However, for this to work you need a very fully planted tank (80%+ of substrate planted). It may not work for sparsely planted tanks or tanks that have a lot of hard scape work.

Green Dust Algae (GDA) - the bane of warm tanks with high light and nutrient levels.

For tanks that use a lot of hard scape work, introducing N/P into the substrate will reduce dust algae problems. This technique uses a rich aquasoil base to supply nitrogen and phosphorus to rooted plants and allows us to completely empty the water column of N and P. A rich aquasoil is paired with a lean water column nutrient dosage - aiming to have no residual N or P in the water column. This approach is particularly effective in aquascapes where all plants are rooted in aquasoil.

In the Iwagumi aquascape below, the carpet draws N and P from the aquasoil areas. The water column is fertilised with a nitrate- and phosphate-free fertiliser (APT 1). This removes N and P from the water column and keeps the glass and hardscape clean of green algae.

Six months after planting the rocks and sand bed are still sparkling.

The same concept can be applied to more heavily planted tanks that require a clean substrate in high light. Plants are fed mostly N/P through the substrate, allowing for a very lean water column.

Fluctuating temperature works better than constantly warm temperatures?

From limited experiments, a tank that fluctuates between 24C and 30C works better than a tank that runs constantly at 30C. The tank benefits partially from being cooled for part of the day.

The tank below is air conditioned at night, suppressing the temperature to a low of 24C, then the temperature rises throughout the day to highs of 30C+. It can be deduced that suppressing the temperature by a few degrees by using fans can also be effective.

Conclusions

When it comes to planted aquariums, ironically the main beneficiaries of a cooler in tropical countries are hobbyists with less expertise. Colder tanks are much easier to manage in terms of algae control and plant melting/adaptation, two major pain points for newer hobbyists.

However, the main factors leading to success in planted tanks are similar whether the tank is colder or warmer, except that warm tanks are more punishing for any mistakes made.

For those seeking optimum growth form and colouration across a wide range of picker species, there is no easy way to cheat the effects of warmer temperatures. Over-compensating with light can produce stronger pigmentation in many species, but can exacerbate algae problems in warm tanks that are already more susceptible to such problems. For this group of enthusiasts, a chiller will give better control over plant aesthetics. The slower growth rate of chilled aquariums also makes it easier to prune and adjust the layout of plants.

Aquarium chillers lower the temperature of the aquarium, but emit a lot of heat themselves. An alternative is to cool the whole room with an air conditioner, but this may not be feasible for many hobbyists. In areas with drier air, fans can be used to lower the temperature by a few degrees, which is also helpful.

Click here to read more on the costs of running chillers in the tropics.