2Hr Tanks are known for their resilience against algae, and we share our approach to algae on our website. However an interesting question came up recently from a reader: do your tanks never have algae? Actually while our tanks are free of algae 90% of the time, there are still several occasions when we face algae problems. Let's explore.
The tank above is a new 2Hr Adventurer (our term for a starter tank without CO2 injection- Guide Here). You can see filamentous algae on the wood and on the leaves of the Anubias and diatoms (the stringy brown mass) on the surface of the substrate.
What is the best thing to do?
Interestingly, in this instance, nothing.
This tank was not fully cycled when we started planting (we had put in the substrate and hardscape and let the filter run, without lights, for 2 weeks, with starter bacteria culture....but 2 weeks is a short amount of time for proper tank cycling...4 would have been better). In addition, a colleague had put in a population of fish (10 tetras and swordtails) without prior quarantine and the entire group had succumbed to white-spots (a classic shock to an already biologically immature new tank). After the dead fish were cleared (2 had decomposed in the filter...which thankfully came with an easy-to-clean prefilter) we knew that algae was inevitable.
In such situations, a good Water Change the 2Hr Way (70%) always helps, which we performed diligently daily for 3 days. This served to limit the damage, but the combination of a partially cycled tank and organic matter gave rise to the algae problem you see in the picture. Importantly, as the tank's infrastructure is sound (suitable plants for a 'low tech' tank, properly-powered canister filter, soil substrate, APT nutrition, medium lights at 70 umols of PAR), the best course of action is simply patience, with increased frequency of water change. We are not using algicides, and have held off from adding more fish till a later date. As with all tanks without CO2 injection, everything develops slowly (really slowly) and we expect that things would take 2 more weeks to stabilise. The algae would then disappear by itself.
The most common mistake at this stage would be to change a bunch of things in the hope of an immediate disappearance of algae: adjusting fertilisation, using all sorts of algicides or adding fancy gadgets. These create flux and hinder the plants from acclimatising to the new tank environment. Healthy plants are in many ways the #1 natural defence against algae...and they are pretty awesome in doing just that. They thrive in stable tank environments and are stressed by erratic changes. Stressed plants trigger algae, and many hobbyists get trapped in a frustrating cycle of recurring algae problems.
It is natural for new tanks to experience algae. It often lasts for weeks (yes-weeks!) in a tank without CO2 injection. Change water the 2Hr Way more frequently, but keep other parameters constant. If you have a sound infrastructure, the algae problem will go away naturally.
After another week, the tank has stabilized considerably. The diatoms have in large part disappeared, but filamentous algae are still present on the leaves of many of the plants. A 'quick fix' would be spot-dose 5% hydrogen peroxide, using an eyedropper, on the areas with algae. This has minimal side effects on plants and livestock, and as hydrogen peroxide breaks down naturally into water and oxygen, there is little harmful residue from the process. But patience is the easier alternative and in this instance we shall just wait for the plants to adjust, strengthen and exert themselves. The filamentous algae would go away naturally.
The hardest part in keeping a tank without CO2 is accepting that patience is part of the deal. In a CO2-deprived environment, plants adjust and adapt alot alot (say that 10 times) more slowly. Algae also takes far longer to disappear.
Importantly this 'delayed response' also works the other way. So the appearance of algae is often linked to events that took place weeks ago, rather than 'yesterday'. This time-delay makes diagnosing issues alot harder in tanks without CO2 injection, so the notion that a tank without CO2 is 'simpler' is not exactly true. It is simpler to set up yes, but actually much harder to upkeep in many ways!
Above: the 2Hr Adventurer Tank, a template for a simple tank without CO2. The consequence of adding plants and fish prematurely (before proper cycling), and starting with a lean plant mass (covering less than 70% of the substrate with plants) is varied forms of 'new tank' algae. In this example, the added trigger was the population of tetra and swordtails that died. With a stable tank infrastructure, the tank would eventually recover and stabilize, but it is certainly taking many weeks to accomplish that!