After I installed new tubes, algae started growing in my tank.
If algae start growing after tube replacement (especially if all of the tubes were replaced at the same time), there are two potential causes:
1) An increase in light due to the new tubes:
Although plants can react to increased amounts of light quickly, plant fertilization must also be adjusted accordingly. A lot of light means stronger plant growth, which in turn results in an increase in the plants' nutrient requirements in terms of CO₂ and trace elements. This applies all the more when reflectors are used additionally above the tubes.
2) Changes in the light spectrum:
Depending on the tubes used previously, installing new tubes can result in a changed spectrum of light. The plants then have to adapt to the new spectrum with their light-harvesting pigments (this does not just refer to chlorophyll, but instead, to so-called accessory pigments as well). This process may take anywhere from a few days to around two weeks. Accordingly, when tubes with a different spectrum are installed, most plants react with a short-term stagnation in growth.
Therefore, it is often advisable not to replace the tubes all at once and instead, to replace one tube at a time at two-week intervals.