Above: a System Shock from an unexpected drop in CO2 triggered plant melt (above- bottom right) and BBA to spawn on the Alternanthera reineckii.

In the picture below, we see the leaves of Samolus parviflorus red- and other plants- suddenly carpeted by fine hair algae- the classic symptom of what we call a 'system shock'.

This happens when changes in environmental parameters induce adaptation stress that weaken plants which become vulnerable to algae.

But I didn't do anything!?

While the impact of some events are expected: e.g. electricity outages and adding a large school of fish (spike in organic waste), system shocks often arise from 3 'silent killers'.

• Slow organic waste accumulation (to a tipping point)
• Gradual reduction in flow (affects distribution of CO2, oxygen & nutrients)
• Drop in CO2

Old Growth / Organic Waste

In mature tanks, the accumulation of old growth (decaying shaded stems and leaves, above) and detritus is easily ignored. Tanks look 'natural' when grown-in, and we associate them with beneficial leaf-litter we see in terrestrial parks. In the tiny closed environment of an aquarium however, old growth and detritus often builds up to a tipping point- a spike in Ammonia, an algae bloom. The cliff-fall is deceptively sudden.

We cover a related aspect in a another article on 'Tank Peak'. When a tank is in full bloom or 'Summer' as we call it, it marks the painful but necessary milestone of trimming and often replanting. Aquatic plants are not perennial, and require regular replanting of the healthy tops.

Reduced Flow

As plants do not move, they rely on water flow to bring oxygen, carbon dioxide and nutrients to their leaves. Filters clog naturally over time, and reduced flow is both invisible and impactful.

Drop in CO2

This is the by far the most impactful (in tanks with CO2 injection) and the most devious. Drop checkers are slow to react, and diffusers can emit visible bubbles and still be be 50% less efficient due to clogging. It is not easy for the eye to notice changes in CO2 mist density.

As CO2 makes up 40-50% of plant mass, it can be akin to an overnight change from a diet of 3 large meals a day to just bread and water. Intermittent fasting may be healthy for humans, but for plants, such a shock inevitably leads to widespread algae as they reprogram their cells to adapt.

How to recover from a system shock

While an algae-infested tank looks irreparable (above- leaves of a Crypt 'flamingo' attacked by BGA, BBA and Hair Algae, it can recover if the plants are fundamentally healthy:

1. Keep parameters stable and let stem plants grow tall. Observe the newest leaves. If they are algae free, recovery is underway. Replant the healthy tops after they grow tall. Remember that portions of the older growth generally cannot and do not recover.
   
   
2. Slow growers like Anubias, Bucephalanda, Alternanthera reineckii etc often have more plasticity than fast growers (i.e they channel more energy to preserving damaged leaves). In these species, spot-doing with APT FIXLITE or FIX can be helpful.
   
   
3. If you have stable tap water (or use RO), more frequent water change after a System Shock can help, as this removes the algae-triggering proteins secreted by plants during the period when 'shocked'.

Remember: a well maintained tank with healthy plants can look irrecoverable, but the opposite is true.

How fast can things recover?

Tanks with high CO2 injection rates are like fast cars. Shocks happen more frequently, but recovery can be quick- often within days or weeks.

Without CO2, overall metabolism is much slower. Shocks are less common, but it can take a long time (months) to recover from one.

Avoid the 3 silent killers

1. Pay attention to old growth. Read this article  on regular replanting.
   
   
2. Take extra effort to clean the filter regularly. It is a chore, but like regular exercise, makes a world of difference over time.
   
   
3. Pay extra attention to CO2. A bubble counter is a must- it tells that the system is running. However, bubble-presence does not mean that CO2 is getting into tank. A clogged diffuser can reduce CO2 by 50% and still emit seemingly normal bubbles. Use the 1pH drop method to gauge CO2 without using test kits. Or invest in a CO2 test kit.