I am feeding once per day in the evening at around 8pm. Is this too late in the day?
Not at all. The time of day is not so important. The most important point is not to overfeed.
I maybe be over feeding as sometimes there is left over food after 2mins, although the Gouramis are always the last to feed & normally take this.
The gouramis will always be last to feed in your tank as they are simply not as fast as the tetras. Obviously the gouramis need to get some food, so if they don't feed within 2 minutes, you will need to leave the food for a bit longer. The 2 minute rule is a guide rather than a hard and fast rule.
I 20% water change every other week & the tank is an established tank with light planting. The nitrate was 25 two weeks ago & now it's 75. Nitrite & Ammonia are both 0.1 and PH at 7.5 - 8.
The rise in nitrate probably suggests that you have been overfeeding, and definitely suggests that you should step up your water changes. I'd recommend 25 - 30% weekly for routine maintenance. You should aim to keep the nitrate level in the tank as close as possible to the nitrate level in your tap water. This is a good guide.
The fact that you have detectable ammonia and nitrite readings suggests a problem. Ammonia and nitrite should always be 0 in an established tank. I suggest doing 30 - 50% water changes twice or 3 times per week for now until the filter catches up with the ammonia / nitrite problem. Keep a close eye on these levels and if they creep up, step up the water changes to compensate. You should aim to keep both levels below 0.25 until the filter catches up and can keep them at 0 for you. Ammonia and nitrite can both be lethal to fish in small quantities, so this is very important.
I plan on doing a 20-30% change weekly from now to try & get the levels down a bit further.
As above, this is fine for routine maintenance, but step up the water changes meantime to deal with ammonia / nitrite.
I am alos using carbon in the filter system to polish the water. Could this be having a detrimental effect on my levels?
It depends how old it is. Carbon will usually become exhausted in between 2 - 6 weeks. After this time, if left in the filter, it may leach toxins back into the water. Carbon is not really necessary for the day to day filtering of your tank and is really just added expense. I would remove it and replace it with some biological media. ie a sponge, ceramic rings etc
Also, should i be squeezing my filters out in tank water with every water change or can i reduce this?
This is unnecessary and can only have a detrimental effect on your filter bacteria. This may explain why your bacteria are struggling to deal with your ammonia and nitrite. You should only clean your sponges when they become dirty enough to restrict the water flow through the filter. Always rinse in tank water and never under the tap.
What is a light feed? A small pinch of flake? A large pinch of flake? or literally, just enough that they eat all the feed in two mins approx??
As above, just as much as the fish can consume in roughly 2 minutes. Again, this is a guide rather than a hard and fast rule.
Hope this helps you.
BTT
edited for spelling
