Do I really need a chiller for my planted aquarium?

Introduction

The temperature for fish tanks can vary widely. In temperate countries it is not common to see unheated tanks hit 18 degree Celsius (64f) and lower and in the tropics, its common to see tanks without a chiller hit an intraday high of 32 degrees Celsius (90f) 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 flipped in the tropics where tank temperatures are too high and often folks may 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 around 10 times more than a heater. Thus, it is cheap and relatively easy to raise tank temperatures but quite costly to lower tank temperatures. For temperate countries facing temperature spikes in summer and for tropical countries that have high temperatures year round, buying a chiller is a serious decision. So, it a chiller really worth it ?

How high is high?

For most tropical planted fish tanks, 22-26 degrees Celsius (72-78f) is the sweet spot where planted aquariums are easy to manage. There isn't a huge difference operating within the sweet zone. Every degree Celsius above this range amplifies the list of upsides and downsides significantly. Keeping below 26C is just a few degrees lower than the average temperatures in the tropics (between 27-32c), however, it does make a significant difference in some aspects.

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

Comparing plant growth forms at 31C vs 24C:

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

Myriophyllum 'Golden' grown in grown in 31C (left) and 24C (right). This plant exhibits whiter coloration in 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 exhibit redder coloration do so more easily in cooler temperatures. Limnophila aromatica is one such plant. Here it is grown in 24C (left) vs 31C (right) under similar dosing regimes and light levels. The plant grown in the cooler tank gains redder coloration more easily.

A few degrees Celsius difference can make a significant impact on plant growth form and coloration for folks that 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 color tone of certain species may not be as deep as compared to plants grown in a cooler tank.

There are also many species such as Alternanthera reineckii that has consistent nice red coloration even at higher temperatures. These bunch are grown in a 31C tank. 

Many species continue to do well in higher temperatures as long as CO2 levels and nutrient needs are met. Several Eriocaulon species can grow well even into the 30s celsius range. Most carpets do well, though HC prefers cooler temperatures. Alternanthera, Hygrophila, and most common Rotala & Ludwigia species do well into the 30 celsius range. Tank above hovers in the 30ish celsius range.

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 from warmer temperatures. Plant and microbial metabolism is increased when temperatures are higher. Tanks cycle and mature faster. When a warm tank is managed well, it can skip new tank algae issues and complete tank cycling faster than a cooler tank.

Aquatic plants grow faster in warmer temperatures, with greater demands on growth input factors such as nutrients and carbon dioxide. Aquascapes can grow in and mature much faster in warmer tanks if the plants are given what they need for growth. Carpets fill in much more quickly and aquascapes can be completed faster and have the grown in look quicker in warmer temperatures provided the plants are given what they require in terms of nutrients and carbon dioxide.

On the flip side, algae also grows much faster in warmer tanks, and runaway algae problems are harder to handle compared to cooler tanks. When things go wrong in a hot tank, it goes wrong in an accelerated manner - plant melting due to poor parameters and algae problems both happen at rapid speed compared to a cooler tank. Aquarists have less reaction time to act, and this severely impacts newer, less experienced aquarists.

For less experienced aquarists, often runaway algae problems becomes the dominant issue, and heat is often blamed for the failure of the tank as a whole. 

Managing algae in warm tanks

Is managing algae much more difficult in warm tanks? Yes, in the sense that algae propagates much more quickly if given the opportunity. However, when managed well, a warm tank can be as algae free as a chilled tank. This will come as a surprise to folks that have always struggled with algae issues in a warm tank.

At the 2hr Aquarist gallery, we have a couple of specially heated tanks that we run at 31-32C (such as above) to test out how heat affects plant growth forms and product performance. The concepts that makes 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 - decay and deterioration happens faster, an ammonia spike from over-feeding for example, that triggers algae hits harder in a warm tank than a cold tank. Run out of CO2? The deterioration in growth and algae spike will hit harder and faster in a warm tank than a cold tank. Left your light on for too long? The algae spike comes faster in the warm tank than the cold tank.

All these mean that we need to run our warm tank with extra sensitivity. There are a few main angles that can help this:

• Plant density gives stability. Having a densely planted tank where the plants outcompete algae is the best defense against algae. Plant densely at the start and also trim and remove old growth to make space for new growth. Warm tanks grow in fast, and can easily make use of plant dominance to deny algae a home. Get this angle right and there is a lot more leeway for errors in other areas.

•  Make sure your CO2 injection is rock solid. Use inline diffusers or reactors and absolutely stay away from in-tank diffusers that clog up more easily and provide poorer CO2 dissolution. Fluctuating CO2 levels create a lot of re-programming in plants and are the main cause of many algae issues. Having good CO2 levels allow tanks to out-grow many problems.

• Aim for lower 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 oxygenation levels and microbial balance in the tank. The overall biological stability of the tank is heavily dependent on those two factors along with adequate surface area for microbial colonization (adequate filter media + substrate zone).

• Bio-active aquasoil substrates contribute more to the biological ecosystem than inert gravel. If using inert substrate, grain sizing of 2-3mm work better than coarse pea gravel, which really does not work well for planted tanks. Aquasoil substrates also allow one 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 pain points in warm tanks. In fully planted tanks, plant dominance usually sets in as the tank matures and the dust algae clears up by itself as the plant gets fully occupied by plants. However, for this to work, it requires a very fully planted tank (80%+ of substrate planted). It may not work for sparsely planted tanks or tanks that have heavy hard scape work.

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

For tanks that make use of heavy hard scape work, moving N/P into the substrate will reduce dust algae issues. This technique uses a rich aquasoil base to substrate feed rooted plants Nitrogen and Phosphorus, and allow us to drain the water column totally of N and P. A rich aquasoil is paired with lean water column nutrient dosing - that aims to have no residual N or P in the water column. This approach is especially effective in aquascapes where all plants are rooted in aquasoil.

In the Iwagumi aquascape below, the carpet feeds off N and P from the aquasoil areas. The water column is fertilized with a Nitrate and Phosphate free fertilizer (APT 1). This drains the water column of N and P and keeps and 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 fully planted tanks that require a clean hardscape in high light. The plants are mostly fed N/P through the substrate, allowing a very lean water column.

Fluctuating temperature works better than constantly warm temperatures?

From limited experiments, having a tank fluctuate between 24C to 30C works better than a tank that runs constantly at 30C. The tank gets partial benefits from being chilled for a portion of the day.

The tank below receives air-conditioning at night, suppressing temperatures to a low of 24C, then temperatures rise throughout the day to highs of 30C+. By inference, suppressing the temperature by a few degrees through the usage of fans can also be effective.

Conclusions

Where planted aquariums are concerned, ironically, the main benefactors of a chiller in tropical countries are hobbyists with less expertise. Colder tanks are much easier to manage - from the point of algae control and plant melting/adaptation, which are two major pain points for newer hobbyists.

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

For folks looking for optimal growth form and coloration across a wide range of picker species, there is no easy way to cheat past the impact of warmer temperatures. Over-compensating with light can give stronger pigmentation in many species, but can exacerbate algae issues in warm tanks that are already more sensitive to such issues. For this group of enthusiasts, a chiller will give better control over plant aesthetics. The slower growth speed of chilled tanks also allows one to prune and align plant bushes in layouts more easily.

Aquarium chillers lower tank temperatures but emit quite a lot of heat themselves. An alternative to this is by chilling the entire room with air-conditioning - however, this may not be feasible for many hobbyists. In areas with drier air, having fans can suppress the temperature by a few degrees and this is helpful also.

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