Post a little long, but want to give enough info so you all can give good advise.
Due to my prolonged illness, my tanks went 2-1/2 months without a water change. Just topping off with RO water.
All tanks are Low Tech, medium to heavily planted, lots of stem plants, and floaters.
I cut my very hard well water 50/50 with RO water that I buy at the grocery - I dose Seachem Flourish, Trace, Potassium once every 10 days or so and Excel at half strength every 4-5 days. While I was sick, all I did was feed the fish and top off water, no fertilizing. Amazing, but plants look pretty good. No fish deaths or illness that I know of in that time. Amazing.
It was a jungle in all three tanks:
2 Fluval Spec V each with a betta and a nerite.
15 gallon that has small fish: CPD, chili rasbora, Otos, Cherry shrimp. It has 2 Aquaclear 20 HOB filters. Eco-Complete.
The two Specs tested pretty good, considering - 0 ammonia and nitrite, about 15 nitrate. But the 15 gal. tested 0 ammonia and nitrite, but 80 nitrate.
I know you are not supposed to deep clean everything at once or it can throw a tank into a cycle. I've only been into this for less than 2 years, though, so could use some advice.
First I recharged the Purigen. I keep one in each tank. Two days ago, I cleaned the Specs - took the bettas out while I did gravel vac, rinsed filter, water down to 1" and refilled. Specs look like they are doing fine. I will go back to weekly 30% changes on them.
But -- the 15 gallon is the one I am not sure what to do about. 80 is pretty high nitrates.
Even before I got sick I was having trouble with the nitrates being over 20, sometimes 40, and I think it was from over feeding. I cut down to once a day feeding, and a LOT less food, about a month before I got sick, but I didn't see much difference in nitrate levels. So I've been working on this for a while, but not doing water change for so long certainly did not help.
Anyway, yesterday, the filters were barely working from being so dirty, so I took them apart, cleaned out the gunk from the pumps, rinsed the sponges, pre-filter (to keep from sucking up shrimp), and put in the refreshed purigen in one filter, and put a new carbon pack in the other. Did a light gravel vac - can't do much more in this tank as the plants are to thick. I took the water down to about 3" above the substrate, then refilled. So maybe 65-70% change. I have not put in any fertilizers yet.
I didn't test the water this morning, but I doubt it will be down that much. With cleaning the filters, Purigen, and the light gravel vac with a pretty large water change…. how soon and how often can I do more water changes to get that nitrate level down to a safe level? Large water changes are bad for the shrimp, correct?
I know the carbon packs are not all that advantageous, and am wondering about adding a second Purigen so both filters on the 15 gal. have one. Would that help with high nitrates?
I want to get that nitrate level down --- but I don't want to screw up the cycle, or do so many water changes to fast and actually harm the fish/shrimp.